Pd and Pt Catalyst Poisoning in the Study of Reaction Mechanisms: What Does the Mercury Test Mean for Catalysis?

The mercury test is a rapid and widely used method for distinguishing truly homogeneous molecular catalysis from nanoparticle metal catalysis. In the current work, using various M
0 and MII complexes of palladium and platinum that are often used in homogeneous catalysis as examples, we demonstrated that the mercury test is generally inadequate as a method for distinguishing between homogeneous and cluster/nanoparticle catalysis mechanisms for the following reasons: (i) the general and facile reactivity of both molecular M0 and MII complexes toward metallic mercury and (ii) the very high and often unpredictable dependence of the test results on the operational conditions and the inability to develop universal quantitatively defined operational parameters. Two main types or mercury-induced transformations, the cleavage of M0 complexes and the oxidative–reductive transmetalation of MII complexes, including a reaction of highly popular MII/NHC complexes, were elucidated using NMR, ESI-MS, and EDXRF techniques. A mechanistic picture of the reactions involving metal complexes was revealed with mercury, and representative metal species were isolated and characterized. Even in an attempt to not overstate the results, one must note that the use of the mercury tests often leads to inaccurate conclusions and complicates the mechanistic studies of these catalytic systems. As a general concept, distinguishing reaction mechanisms (homogeneous vs cluster/nanoparticle) by using catalyst poisoning requires careful rethinking in the case of dynamic catalytic systems.

Reversible leaching of palladium nanoparticles occurs in a variety of catalytic reactions including cross-couplings, amination, the Heck reaction, etc. It is complemented by capturing of soluble palladium species on the surface of nanoparticles and de novo formation of nanoparticles from Pd precatalysts. We report here a detailed computational study of leaching/capture pathways and analysis of related stabilization energies. We demonstrate the validity of the "cocktail-of-species" model for the description of Pd catalysts in ArX oxidative addition-dependent reactions. Three pools of Pd species were evaluated, including (1) the pool of catalytically active Pd nanoparticles with a high concentration of surface defects, (2) the pool of monomeric and oligomeric L[ArPdX]
nL species, and (3) the pool of irreversibly deactivated Pd. Stabilization by ArX oxidative addition, coordination of base species, and binding of X− anions (derived from salt additives) were found to be crucial for "cocktail"-type systems, and the corresponding reaction energies were estimated. An inherent process of ArX homocoupling, leading to the formation of Pd halides that require re-activation, was considered as well. The pool of irreversibly deactivated Pd comprises nanoparticles with (1 1 1) and (1 0 0) facets and Pd in the bulk form. The study is based on DFT modeling and specifies the role of Pd nanoparticles in (quasi )homogeneous coupling reactions involving ArX reagents.

Calcium carbide, a stable solid compound composed of two atoms of carbon and one of calcium, has proven its effectiveness in chemical synthesis, due to the safety and convenience of handling the C≡C acetylenic units. The areas of CaC
2 application are very diverse, and the development of calcium‐mediated approaches resolves several important challenges. This Review aims to discuss the laboratory chemistry of calcium carbide, and to go beyond its frontiers to organic synthesis, life sciences, materials and construction, carbon dioxide capturing, alloy manufacturing, and agriculture. The recyclability of calcium carbide and the availability of large‐scale industrial production facilities, as well as the future possibility of fossil‐resource‐independent manufacturing, position this compound as a key chemical platform for sustainable development. Easy regeneration and reuse of the carbide highlight calcium‐based sustainable chemical technologies as promising instruments for total carbon recycling.

Sleeping Giant” of Sustainable Chemistry, Awaken?

Bring on the subs! Biorefining will be realized by using two different approaches: the production of new biobased molecular targets or sustainable access to traditional base and commodity chemicals. Awakening of 5‐hydroxymethylfurfural (HMF) can be expected with different probabilities, depending on the approach chosen to create a sustainable future.

An efficient two-step procedure to get synthetically useful sulfur-functionalized dienes is evaluated. The overall transformation can be classified as an atom-economic hydrothiolation of alkynes followed by elimination of water at the dehydration step. Taking the alkynes hydrofunctionalization reaction as a representative example, critical analysis from the point of view of quantitative green metrics was carried out and key stumbling blocks in the area of atom-economic transformations were discussed. Ecological acceptability of the whole process was assessed by thorough examination of the yields and careful adjustment of the synthetic conditions, considering the opportunities for waste minimization. Careful optimization of the reaction conditions was followed by selection of environmentally friendly protocols for accessing pure product. Green metrics of synthetic procedures as well as different isolation techniques (column chromatography, dry column chromatography, extraction, and distillation) were comparatively analyzed to afford minimization of waste and improve efficiency. For the first time, quantitative green metrics and life cycle assessment were applied and optimized for a very popular atom-economic functionalization process.

Phantom Reactivity in Organic and Catalytic Reactions as a Consequence of Microscale Destruction and Contamination-Trapping Effects of Magnetic Stir Bars

Magnetic stir bars are routinely used by every chemist doing synthetic or catalytic transformations in solution. Each bar lasts for months or years, as the regular PTFE (polytetrafluoroethylene) coating is believed to be highly durable, inert, and resistant to multiple washings and cleanings. By using electron microscopy, we found out quite unexpectedly that the surface of magnetic stir bars is susceptible to microscale destruction and forms various types of defects. These microscopic defects effectively trap and accumulate trace amounts of active components from reaction mixtures, most notably metal species. Trapped in surface defects, the impurities escape elimination by washing and cleaning, thus remaining on the surface. FE-SEM/EDX analysis shows that the surface of used stir bars is littered with contaminants representing a variety of metals (Pd, Pt, Au, Fe, Co, Cr, etc.). ESI-MS monitoring corroborates the transfer of the trace metal species to reaction mixtures, while chemical tests indicate their significant catalytic activity. A theoretical DFT study reveals a remarkably high binding energy of metal atoms to the PTFE surface, especially in cases of local mechanical disruption or chemical influence. A plausible mechanism of PTFE surface contamination is suggested, and the results show that metal contamination of reusable polymer-coated labware is greatly underestimated. The present study suggests that corresponding control experiments with an unused stir bar (to avoid misinterpretations due to the influence of contamination of magnetic stir bars) are a "must do" for reporting high-performance catalytic reactions, reactions with low catalyst loadings, metal-catalyst-free reactions, and mechanistic studies.

Towards Improved Biorefinery Technologies: 5‐Methylfurfural as a Versatile C6‐Platform for Biofuels Development

Low chemical stability and high oxygen content limits utilization of bio‐based platform chemical 5‐(hydroxymethyl)furfural (HMF) in biofuels development. In this work, Lewis‐acid‐catalyzed conversion of renewable 6‐deoxy sugars leading to formation of more stable 5‐methylfurfural (MF) is carried out with high selectivity. Besides its higher stability, MF is a deoxygenated analogue of HMF with increased C:O ratio. A highly selective synthesis of the innovative liquid biofuel 2,5‐dimethylfuran starting from MF under mild conditions is described. Superior synthetic utility of MF against HMF in benzoin and aldol condensation reactions leading to long‐chain alkane precursors is demonstrated.

Synthesis of 2-Azidomethyl-5-ethynylfuran: A New Bio-Derived Self-Clickable Building Block

2-Azidomethyl-5-ethynylfuran, a new ambivalent compound with both azide and alkyne moieties that can be used as a self-clickable monomer, is synthesized starting directly from renewable biomass. The reactivity of the azide group linked to furfural is tested via the efficient preparation of a broad range of furfural-containing triazoles in good to excellent yields using a 'green' copper(I)-catalyzed azide–alkyne cycloaddition procedure. Access to new bio-based chemicals and oligomeric materials via a click-chemistry approach is also demonstrated using this bio-derived building block.

A well‐established oxidative addition of organic halides (R‐X) to N‐heterocyclic carbene (NHC) complexes of palladium(0) leads to formation of (NHC)(R)Pd
II(X)L species, the key intermediates in a large variety of synthetically useful cross‐coupling reactions. Typical consideration of the cross‐coupling catalytic cycle is based on the assumption of intrinsic stability of these species, where the subsequent steps involve coordination of the second reacting partner. Thus, high stability of the intermediate (NHC)(R)PdII(X)L species is usually taken for granted. In the present study it is discussed that such intermediates are prone to non‐classical R‐NHC intramolecular coupling process (R = Me, Ph, Vinyl, Ethynyl) that results in removal of NHC ligand and generation of another type of Pd catalytic system. DFT calculations (BP86, TPSS, PBE1PBE, B3LYP, M06, wB97X‐D) clearly show that outcome of R‐NHC coupling process is not only determined by chemical nature of the organic substituent R, but also strongly depends on the type of solvent. The reaction is most favorable in polar solvents, whereas the non‐polar solvents render the products less stable.

In situ transformations of Pd/NHC complexes to colloidal Pd nanoparticles studied for N-heterocyclic carbene ligands of different nature

R–NHC coupling was previously considered as a process of degradation of M/NHC species, however recent studies have pointed out that it may be responsible for generation of catalytically active NHC-free complexes or/and metallic nanoparticles. Therefore, a detailed and systematic study of R-NHC coupling for various carbene ligands is an important topic. In the present article this process has been studied for reactive aryl iodide coupling partners by a combination of quantum chemical calculations and continuous reaction monitoring via pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS). DFT calculations revealed strong tendency of (NHC)Pd(Ph)(I)DMF complexes bearing various N-heterocyclic carbene ligands (NHC) to undergo Ph–NHC coupling. Calculated energy barriers of these reactions lie in the range of 17.9 – 25.1 kcal/mol. Ph–NHC coupling is thermodynamically more favorable for the complexes containing unsaturated NHC ligands with bulky substituents. NBO analysis has suggested that the process of Ph–NHC formation is similar for different NHC ligands. In order to confirm theoretical studies, a series of ESI-MS reaction monitoring experiments was performed for (NHC)Pd(I)2(Py) and (NHC)Pd(Cl)(η3-1-Ph-C3H4) complexes interacting with iodobenzene, where Ph–NHC coupling products were observed in all cases. As a direct experimental evidence, formation of colloidal Pd-containing nanoparticles was observed in situ for different Pd/NHC complexes in the studied reaction mixtures.

Switchable Ni-Catalyzed Bis-Thiolation of Acetylene with Aryl Disulfides as an Access to Functionalized Alkenes and 1,3-Dienes

The article provides the first example of metal-catalyzed aryl disulfide addition to unsubstituted acetylene. The use of inexpensive Ni(acac)2 precatalyst with phosphine ligands results in competitive formation of
Z-1,2-bis(arylthio)ethenes and Z,Z-1,4-bis(arylthio)buta-1,3-dienes. The process with the PPhCy2 as a ligand results in selective formation of diene molecular skeletons. Replacement of PPhCy2 with the PPh3 switches the reaction toward formation of alkenes. The use of substituted phenyl disulfides does not affect the selectivity and allows obtaining alkenes or dienes in good to high yields. Mechanistic investigations reveal major differences on the catalyst activation stage depending on the nature of phosphine ligand. Key novel point is to carry out video-monitoring of catalyst evolution with electron microscopy, which revealed the dynamic nature of the catalytic system and showed that the ligand played a prominent role in formation of the catalytically active phase. For PPh3, the development of catalytically active species proceeds through nickel thiolate [Ni(SAr)2]n formation, which renders the system heterogeneous. In contrast to PPh3, the PPhCy2 ligand promotes direct activation of the catalyst in its molecular form without disturbing the homogeneous state of the system.

Pseudo‐Solid‐State Suzuki‐Miyaura Reaction and the Role of Water Formed by Dehydration of Arylboronic Acid

Solvent‐free reactions belong to a very attractive area of organic chemistry. The solvent‐free Suzuki‐Miyaura coupling is of special importance due to the problem of catalyst leaching in the presence of a solvent. This study investigates the course of reaction of solid aryl halides with arylboronic acids in the absence of a solvent and without any liquid additives. For the first time, a number of important conditions for performing a solid‐state Suzuki‐Miyaura reaction were analyzed in details. The results indicate a prominent role of water, which is formed as a by‐product in the side reaction of arylboronic acid trimerization. Electron microscopy study revealed surprising changes occurring within the reaction mixture during the reaction and indicated the formation of spherical nano‐sized particles containing the reaction product. Catalyst recycling was easily performed in the developed system and the product was isolated by sublimation, thus providing a possibility to completely avoid the use of solvents at all stages.

Systematic Study of the Behavior of Different Metal and Metal-Containing Particles under the Microwave Irradiation and Transformation of Nanoscale and Microscale Morphology

In recent years, the application of microwave (MW) irradiation has played an increasingly important role in the synthesis and development of high performance nanoscale catalytic systems. However, the interaction of microwave irradiation with solid catalytic materials and nanosized structures remains a poorly studied topic. In this paper we carried out a systematic study of changes in morphology under the influence of microwave irradiation on nanoscale particles of various metals and composite particles, including oxides, carbides, and neat metal systems. All systems were studied in the native solid form without a solvent added. Intensive absorption of microwave radiation was observed for many samples, which in turn resulted in strong heating of the samples and changes in their chemical structure and morphology. A comparison of two very popular catalytic materials—metal particles (M) and supported metal on carbon (M/C) systems—revealed a principal difference in their behavior under microwave irradiation. The presence of carbon support influences the heating mechanism; the interaction of substances with the support during the heating is largely determined by heat transfer from the carbon. Etching of the carbon surface, involving the formation of trenches and pits on the surface of the carbon support, were observed for various types of the investigated nanoparticles.

A catalytic system based on OX-1 metal–organic framework nanosheets is reported, incorporating catalytically active palladium (Pd) species. The Pd@OX-1 guest@host system is rapidly synthesized via a one-step single-pot supramolecular assembly, with the possibility of controlling the Pd loading. The structures of the resulting framework and of the active Pd species before and after catalytic reactions are studied in detail using a wide variety of techniques including synchrotron radiation infrared spectroscopy, inelastic neutron scattering, and X-ray absorption spectroscopy. Crystals of the resulting Pd@OX-1 composite material contain predominantly atomic and small cluster Pd species, which selectively reside on benzene rings of the benzenedicarboxylate (BDC) linkers. The composites are shown to efficiently catalyze the Suzuki coupling and Heck arylation reactions under a variety of conditions. Pd@OX-1 further shows potential to be recycled for at least five cycles of each reaction as well as an ability to recapture active Pd species during both catalytic reactions.

Evaluation of phytotoxicity and cytotoxicity of industrial catalyst components (Fe, Cu, Ni, Rh and Pd): A case of lethal toxicity of a rhodium salt in terrestrial plants

Until recently, chemical derivatives of platinum group metals have not been in a systematic direct contact with living organisms. The situation has changed dramatically due to anthropogenic activity, which has led to significant redistribution of these metals in the biosphere. Millions of modern cars are equipped with automotive catalytic converters, which contain rhodium, palladium and platinum as active elements. Everyday usage of catalytic technologies promotes the propagation of catalyst components in the environment. Nevertheless, we still have not accumulated profound information on possible ecotoxic effects of these metal pollutants. In this study, we report a case of an extraordinarily rapid development of lethal toxicity of a rhodium (III) salt in the terrestrial plants
Pisum sativum, Lupinus angustifolius and Cucumis sativus. The growth stage, at which the exposure occurred, had a crucial impact on the toxicity manifestation: at earlier stages, RhCl3 killed the plants within 24 h. In contrast, the salt was relatively low-toxic in human fibroblasts. We also address phytotoxicity of other common metal pollutants, such as palladium, iron, nickel and copper, together with their cytotoxicity. None of the tested compounds exhibited phytotoxic effects comparable with that of RhCl3. These results evidence the crucial deficiency in our knowledge on environmental dangers of newly widespread metal pollutants.

A novel methodology for the preparation of trideuterovinyl derivatives of high purity directly from alcohols, thiols, and NH-compounds was developed. Commercially available calcium carbide and D
2O acted as a D2-acetylene source, and DMSO-d 6 was used to complete the formation of the D2C=C(D)–X fragment (X = O, S, N). Polymerization of a selected trideuterovinylated compound showed a very promising potential of these substances in the synthesis of labeled polymeric materials. Biological activity of the synthesized trideuterovinyl derivatives was evaluated and the results indicated a significant increase of cytotoxicity upon deuteration.

Exploring the performance of nanostructured reagents with organic-group-defined morphology in cross-coupling reaction

The great impact of the nanoscale organization of reactive species on their performance in chemical transformations creates the possibility of fine-tuning of reaction parameters by modulating the nano-level properties. This methodology is extensively applied for the catalysts development whereas nanostructured reactants represent the practically unexplored area. Here we report the palladium- and copper-catalyzed cross-coupling reaction involving nano-structured nickel thiolate particles as reagents. On the basis of experimental findings we propose the cooperative effect of nano-level and molecular-level properties on their reactivity. The high degree of ordering, small particles size, and electron donating properties of the substituents favor the product formation. Reactant particles evolution in the reaction is visualized directly by dynamic liquid-phase electron microscopy including recording of video movies. Mechanism of the reaction in liquid phase is established using on-line mass spectrometry measurements. Together the findings provide new opportunities for organic chemical transformations design and for mechanistic studies.

Revealing the Unusual Role of Bases in Activation/Deactivation of Catalytic Systems: O–NHC Coupling in M/NHC Catalysis

Numerous reactions are catalyzed by complexes of metals (M) with N-heterocyclic carbene (NHC) ligands, typically in the presence of oxygen bases, which significantly shape the performance. It is generally accepted that bases are required for either substrate activation (exemplified by transmetallation in the Suzuki cross-coupling), or HX capture (e.g. in a variety of C–C and C-heteroatom couplings, the Heck reaction, C–H functionalization, heterocyclizations, etc.). This study gives insights into the behavior of M(II)/NHC (M = Pd, Pt, Ni) complexes in solution under the action of bases conventionally engaged in catalysis (KOH, NaOH, t-BuOK, Cs2CO3, K2CO3, etc.). A previously unaddressed transformation of M(II)/NHC complexes under conditions of typical base-mediated M/NHC catalyzed reactions is disclosed. Pd(II) and Pt(II) complexes widely used in catalysis react with the bases to give M(0) species and 2(5)-oxo-substituted azoles via an O–NHC coupling mechanism. Ni(NHC)2X2 complexes hydrolyze in the presence of aqueous potassium hydroxide, and undergo the same O–NHC coupling to give azolones and metallic nickel under the action of t-BuOK under anhydrous conditions. The study reveals a new role of NHC ligands as intramolecular reducing agents for the transformation of M(II) into "ligandless" M(0) species. This demonstrates that the disclosed base-mediated O–NHC coupling reaction is integrated into the catalytic M/NHC systems and can define the mechanism of catalysis (molecular M/NHC vs. "NHC-free" cocktail-type catalysis). A proposed mechanism of the revealed transformation includes NHC-OR reductive elimination, as implied by a series of mechanistic studies including 18O labeling experiments.

“Solvent-in-Salt” Systems for Design of New Materials in Chemistry, Biology and Energy Research

Inorganic and organic "solvent-in-salt" (SIS) systems have been known for decades but have attracted significant attention only recently. Molten salt hydrates/solvates have been successfully employed as non-flammable, benign electrolytes in rechargeable lithium-ion batteries leading to a revolution in battery development and design. SIS with organic components (for example, ionic liquids containing small amounts of water) demonstrate remarkable thermal stability and tunability, and present a class of admittedly safer electrolytes, in comparison with traditional organic solvents. Water molecules tend to form nano- and microstructures (droplets and channel networks) in ionic media impacting their heterogeneity. Such microscale domains can be employed as microreactors for chemical and enzymatic synthesis. In this review, we address known SIS systems and discuss their composition, structure, properties and dynamics. Special attention is paid to the current and potential applications of inorganic and organic SIS systems in energy research, chemistry and biochemistry. A separate section of this review is dedicated to experimental methods of SIS investigation, which is crucial for the development of this field.

Biomass processing wastes (humins) are anticipated to become a large‐tonnage solid waste in the nearest future, owing to the accelerated development of renewable technologies based on utilization of carbohydrates. In this work, the utility of humins as a feedstock for the production of activated carbon by various methods (pyrolysis, physical and chemical activation, or combined approaches) was evaluated. The obtained activated carbons were tested as potential electrode materials for supercapacitor applications and demonstrated combined micro‐ and mesoporous structure with a good capacitance of 370 Fg−1 (at a current density of 0.5 Ag−1) and good cycling stability with a capacitance retention of 92% after 10,000 charge/discharge cycles (at 10 Ag−1 in 6 M aqueous KOH electrolyte). Applicability of the developed activated carbon for practical usage as a supercapacitor electrode material was demonstrated by its successful utilization in symmetric two‐electrode cells and powering electric devices. These findings provide a new approach to deal with the problem of sustainable wastes utilization and to advance challenging energy storage applications.

Ten-Fold Boost of Catalytic Performance in Thiol-Yne Click Reaction Enabled by a Palladium Diketonate Complex with a Hexafluoroacetylacetonate Ligand

Palladium complexes with fluorinated acetylacetonate chelating ligands were studied as catalysts for alkyne hydrothiolation. A ten-fold increase in the catalytic efficiency was achieved by using 0.1 mol% of
Pd(hfpd)2 complex (hfpd = hexafluoroacetylacetonate) with a variety of thiol–yne coupling partners. The principal possibility of a hundred-fold increase in the efficiency of Pd-catalyzed Markovnikov-type RSH addition with 0.01 mol% of the catalyst was successfully achieved with the hfpd ligand for the first time. The hexafluoroacetylacetonate chelating ligand not only enhanced the affinity of palladium centers to the triple bond of acetylene, but also stabilized the catalytic system against formation of insoluble polymeric [Pd(SPh)2]n species, thus ensuring that the reaction operates homogeneously. Utilizing other diketonate ligands resulted in cocktail-type catalysis with variable and poorly predictable contributions of homogeneous and heterogeneous pathways.

Synthesizing chemicals and materials based on renewable sources is one of the main tasks of modern science. Carbohydrates represent excellent renewable natural raw materials, that are eco-friendly, inexpensive and biologically compatible. Herein, we developed a green vinylation procedure for carbohydrates using readily available calcium carbide. Various carbohydrates were utilized as starting materials resulting in mono-, di- and tetra-vinyl ethers in high to excellent yields (81-92 %). The synthesized bio-based vinyl ethers were utilized as monomers in free radical and cationic polymerizations. A unique combination of smooth surface and intrinsic microcompartments was achieved in the synthesized materials. Two types of bio-based materials were prepared involving microspheres and "Swiss cheese" polymers. Scanning electron microscopy with built-in ion beam cutting was applied to reveal the spatial hierarchical structures in three-dimensional space.

Recent advances in the area of biomass-derived C6-furanic platform chemicals for sustainable biomass processing are analyzed focusing on chemical reactions important for development of practical applications and materials science. Among the chemical processes currently being studied, tuning the amount of oxygen-containing functional groups remains the most active research direction. Production of efficient fuels requires the removal of oxygen atoms (reduction reactions), whereas utilization of biomass-derived furanic derivatives in material science points out the importance of oxidation in order to form dicarboxylic derivatives. Stimulated by this driving force, oxidation and reduction of 5-(hydroxymethyl)furfural (HMF) are nowadays massively studied. Moreover, these fundamental transformations are often used as model reactions to test new catalysts, and HMF transformations guide the development of new catalytic systems. From the viewpoint of organic synthesis, highly diverse chemical reactivity is explored and a number of bioderived synthetic building blocks with different functional groups are now accessible. This Perspective covers the most recent literature (since Jan 2017) to highlight the emerging research trends.

Fast and Slow Release of Catalytically Active Species in Metal/NHC Systems Induced by Aliphatic Amines

The behavior of ubiquitously used nickel, palladium, and platinum complexes containing N-heterocyclic carbene ligands was studied in solution in the presence of aliphatic amines. Transformation of M(NHC)X
2L complexes readily occurred according to the following reactions: (i) release of the NHC ligand in the form of azolium salt and formation of metal clusters or nanoparticles and (ii) isomerization of mono-NHC complexes M(NHC)X2L to bis-NHC derivatives M(NHC)2X2. Facile cleavage of the M–NHC bond was observed and provided the possibility for fast release of catalytically active NHC-free metal species. Bis-NHC metal complexes M(NHC)2X2were found to be significantly more stable and represented a molecular reservoir of catalytically active species. Slow decomposition of the bis-NHC complexes by removal of the NHC ligands (also in the form of azolium salts) occurred, generating metal clusters or nanoparticles. The observed combination of dual fast- and slow-release channels is an intrinsic latent opportunity of M/NHC complexes, which balances the activity and durability of a catalytic system. The fast release of catalytically active species from M(NHC)X2L complexes can rapidly initiate catalytic transformation, while the slow release of catalytically active species from M(NHC)2X2 complexes can compensate for degradation of catalytically active species and help to maintain a reliable amount of catalyst. The study clearly shows an outstanding potential of dynamic catalytic systems, where the key roles are played by the lability of the M–NHC framework rather than its stability.

A facile direct deposition approach for the preparation of recyclable Pd/C catalysts simply by stirring a solution of Pd
2dba3 with a suitable carbon material was evaluated. An extraordinary rapid catalyst preparation procedure (< 5 min) under mild conditions and its excellent performance in cross-coupling and hydrogenation reactions were demonstrated. The key point for catalyst design was to directly deposit Pd(0) centers onto highly accessible surface area and to avoid ill-defined Pd(II)/Pd(0) states.

Oxidative addition of organic halides (R–X) to (NHC)Pd
0L complexes is involved in numerous metal-catalyzed reactions, and this step is expected to afford (NHC)PdII(R)(X)L intermediate complexes. However, these complexes may undergo further transformation via R–NHC coupling, which removes the NHC ligands from the metal and results in the generation of "bare" NHC-free metal species. The comparative theoretical study carried out in the present work revealed that the kinetic and thermodynamic stability of the (NHC)PdII(R)(X)L oxidative addition intermediates depends strongly on the nature of the organic group R. The predicted reactivity in the R–NHC coupling process decreases in the following order: R = Vinyl > Ethynyl > Ph > Me. Accordingly, for R = Me, a classical (NHC)PdII(R)(X)L intermediate can be expected as a product of the oxidative addition step, whereas for R = Ph, the outcome of the oxidative addition may already contain the NHC-free palladium complex. For R = Ethynyl, comparable amounts of both complexes should be formed, while for R = Vinyl, the NHC-free palladium complex can be the major product of the oxidative addition process. Unusual thermodynamic and kinetic instability of the (NHC)Pd(vinyl)(X)L complex and the tendency to vinyl–NHC coupling predicted by the computational modeling has been confirmed by experimental measurements with online mass spectrometric reaction monitoring. Thus, the outcome of the oxidative addition strongly depends on the type of organic group R and the R–NHC coupling process greatly influences the activity and stability of metal catalysts.

High-Performance Synthesis of Phosphorus-Doped Graphene Materials and Stabilization of Phosphoric Micro- and Nanodroplets

A thermally induced cascade process leading to the formation of stable micro- and nanometer-size phosphoric droplets was developed starting from a molecular precursor. Microwave-induced pyrolysis of 1,2,3,4,5-pentaphenylphosphole oxide proceeded through a series of subsequent transformations involving formation of phosphorus-doped graphene oxide layers, seeding of carbon surface with phosphorus centers, and assembling of stable droplets. A complex nanostructured organization of the material was established in a remarkably short time of 3 min, and the process was performed in a thermally induced manner using microwave irradiation. High stability of the liquid phosphoric structures on the surface of doped graphene oxide over a few-month period was demonstrated, as well as under challenging conditions in organic solvents (chloroform, methylene chloride, or toluene media) and even under sonication. Detailed examination of this material by electron microscopy and a number of analytical methods showed its unique organization at the nanoscale, whereas computational modeling revealed unusually strong binding of phosphorus oxide P
4O10 to the graphene surface. The study demonstrates a fascinating opportunity to access a complex nanostructured multicomponent material from a single and easily available molecular precursor.

Storage and handling of toxic wastes is a top-priority challenge for sustainable development and public health. In recent years, the risk of irreversible environmental pollution has been increasing gradually, necessitating the development of new concepts in this highly demanding area. Here, we report a flexible approach to address the problem using tunable ionic liquids as a carrier and storage medium for chemicals. Encapsulation in microscale tunable media surrounded by an inert ionic liquid facilitates the efficient capture of chemicals. The adaptive character of the designed microscale compartments opens new possibilities for the waste management of chemicals of a diverse nature. Real-time field-emission scanning electron microscopy was used to visualize the formation of microscale compartments upon the sequestration of chemicals in ionic liquids. Ionic liquids captured the chemicals better than traditional organic solvents or water; moreover, the chemicals subsequently could be effectively extracted for destruction or utilization. Our work presents a new model for the sustainable management of chemical wastes; the concept was evaluated for a number of multiton chemicals currently affecting our environment.

For the first time, extraction process in ionic liquids was visualized by direct electron microscopy observation. Microscopy images revealed the micro-heterogeneous nature of the studied extraction systems. Depending on the nature of ionic liquids and studied compounds, four main micro-scale areas were observed: a) uniform homogeneous phase; b) microcompartments in the liquid phase; c) solid microinclusions on the phase boundary; and d) solid microinclusions inside the separated microphases. The microscopic monitoring showed stepwise sequence of the extraction process, and the retention ability of the ionic liquid–water system decreased in the following order: homogeneous phase > microcompartments > solid microinclusions.

Fundamental importance of ionic interactions in the liquid phase: A review of recent studies of ionic liquids in biomedical and pharmaceutical applications

In recent years, research on ions and ionic interactions in solution has become a leading scientific direction, and this advance has been especially pronounced in the field of ionic liquids, particularly coupled with the studies on their toxicity and biological activity. The focus of these studies has clearly shifted from environmental dangers to feasible applications of these unique substances in biotechnology and pharmacy. In this review, we address the rapidly developing area of ionic liquid-related research and discuss the most recent studies to emphasize the state-of-the-art tendencies. Fundamental research on ionic species in the liquid phase drives new conceptual development of ionic drugs and pharmaceutical substances. Mechanistic knowledge on ionic interactions in aqueous media stimulates the appearance of innovative projects in medicine and biochemistry.

Acetylene in Organic Synthesis: Recent Progress and New Uses

Recent progress in the leading synthetic applications of acetylene is discussed from the prospect of rapid development and novel opportunities. A diversity of reactions involving the acetylene molecule to carry out vinylation processes, cross-coupling reactions, synthesis of substituted alkynes, preparation of heterocycles and the construction of a number of functionalized molecules with different levels of molecular complexity were recently studied. Of particular importance is the utilization of acetylene in the synthesis of pharmaceutical substances and drugs. The increasing interest in acetylene and its involvement in organic transformations highlights a fascinating renaissance of this simplest alkyne molecule.

[3 + 2]-Cycloaddition of in Situ Generated Nitrile Imines and Acetylene for Assembling of 1,3-Disubstituted Pyrazoles with Quantitative Deuterium Labeling

A novel synthetic methodology for the preparation of 1,3-disubstituted pyrazoles from
in situgenerated nitrile imines and acetylene is reported. The reactions are performed in a simple two-chamber reactor. One part of the reactor is loaded with hydrazonoyl chloride precursors of active nitrile imine species and a base. The other part is used to generate acetylene from CaC2 and water. Partitioning of the reactants improves the yields of desired pyrazoles up to 99% and simplifies their isolation to a simple procedure of solvent evaporation. The approach requires no complex equipment and utilizes inexpensive, safe, and easy to handle calcium carbide as a starting material. A model deuterium incorporation is carried out according to the developed methodology, producing a series of novel 4,5-dideuteropyrazoles with excellent deuterium enrichment. Theoretical calculations on reaction mechanism and characterization of possible intermediate structures were performed.

In this work, a novel synthetic methodology for the one-pot preparation of isoxazoles directly from the reaction of calcium carbide with aldoximes is reported. Calcium carbide acts as a safe and inexpensive acetylene source and, in addition, as a source of the Ca(OH)2 base to enable the generation of nitrile oxide. Various 3-substituted isoxazoles were synthesized from the corresponding aldoximes in good yields (up to 95%) and a series of new deuterated 4,5-dideuteroisoxazoles were prepared.

Vinylation of a Secondary Amine Core with Calcium Carbide for Efficient Post-Modification and Access to Polymeric Materials

We developed a simple and efficient strategy to access N-vinyl secondary amines of various naturally occurring materials using readily available solid acetylene reagents (calcium carbide, KF, and KOH). Pyrrole, pyrazole, indoles, carbazoles, and diarylamines were successfully vinylated in good yields. Cross-linked and linear polymers were synthesized from N-vinyl carbazoles through free radical and cationic polymerization. Post-modification of olanzapine (an antipsychotic drug substance) was successfully performed.

Additive manufacturing with fused deposition modeling (FDM) is currently optimized for a wide range of research and commercial applications. The major disadvantage of FDM-created products is their low quality and structural defects (porosity), which impose an obstacle to utilizing them in functional prototyping and direct digital manufacturing of objects intended to contact with gases and liquids. This article describes a simple and efficient approach for assessing the quality of 3D printed objects. Using this approach it was shown that the wall permeability of a printed object depends on its geometric shape and is gradually reduced in a following series: cylinder > cube > pyramid > sphere > cone. Filament feed rate, wall geometry and G-code-defined wall structure were found as primary parameters that influence the quality of 3D-printed products. Optimization of these parameters led to an overall increase in quality and improvement of sealing properties. It was demonstrated that high quality of 3D printed objects can be achieved using routinely available printers and standard filaments.

3D Printing with Biobased PEF for Carbon Neutral Manufacturing

We demonstrate the utility of 100% biomass-derived poly(ethylene-2,5-furandicarboxylate) (PEF) as an efficient material for Fused Deposition Modeling (FDM) 3D printing. A complete cycle from cellulose to printed object has been performed. PEF-printed objects created in the present study demonstrated higher chemical resistance than objects printed with commonly available materials (ABS, PLA, PETG). The studied PEF polymer has shown key advantages for 3D printing: optimal adhesion, thermoplasticity, lack of delamination and low heat shrinkage. The high thermal stability of PEF and relatively low temperature that are necessary for extrusion are optimal for recycling printed objects and minimizing waste. Several successive cycles of 3D-printing and recycling were successfully demonstrated. The suggested approach for extending additive manufacturing to carbon neutral materials opens a new direction in the field of sustainable development.

Understanding Active Species in Catalytic Transformations: from Molecular Catalysis to Nanoparticles, Leaching, “Cocktails” of Catalysts and Dynamic Systems

In the present review, we consider the transformations of molecular catalysts, leaching, aggregation and various interconversions of metal complexes, clusters and nanoparticles that occur during catalytic processes. The role of catalyst evolution and the mechanistic picture of "cocktail"-type systems are considered from the perspective of the development of a new generation of efficient, selective and re-usable catalysts for synthetic applications. Rational catalyst development and the improvement of catalyst performance cannot be achieved without an understanding of the dynamic nature of catalytic systems.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine

Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in the form of ionic liquid species. The main aim of this Review is to attract a broad audience of chemical, biological, and medical scientists to study advantages of ionic liquid pharmaceutics. Overall, the discussed data highlight the importance of the research direction defined as "Ioliomics", studies of ions in liquids in modern chemistry, biology, and medicine.

A Solid Acetylene Reagent with Enhanced Reactivity: Fluoride-Mediated Functionalization of Alcohols and Phenols

The direct vinylation of an OH group in alcohols and phenols was carried out utilizing a novel CaC
2/KF solid acetylene reagent in a simple K2CO3/KOH/DMSO system. The functionalization of a series of hydroxyl-group-containing substrates and the post-modification of biologically active molecules were successfully performed using standard laboratory equipment, providing straightforward access to the corresponding vinyl ethers. The overall process developed involves an atom-economical addition reaction employing only inorganic reagents, which significantly simplifies the reaction set-up and the isolation of products. A mechanistic study revealed a dual role of the F− additive, which both mediates the surface etching/renewal of the calcium carbide particles and activates the CC bond towards the addition reaction. The development of the fluoride-mediated nucleophilic addition of alcohols eliminates the need for strong bases and may substantially extend the areas of application of this attractive synthetic methodology due to increasing functional group tolerance. As a replacement for dangerous and difficult to handle high-pressure acetylene, we propose the solid reagent CaC2/KF, which is easy to handle, does not require dedicated laboratory equipment and demonstrates enhanced reactivity of the acetylenic triple bond. Theoretical calculations have shown that fluoride-mediated activation of the hydroxyl group towards nucleophilic addition significantly reduces the activation barrier and facilitates the reaction.

Efficient Route for the Construction of Polycyclic Systems from Bioderived HMF

The first synthesis of tricyclic compounds from biobased 5-hydroxymethylfurfural (HMF) is described. The Diels-Alder reaction was used to implement the transition from HMF to non-planar framework, which possessed the structural cores of naturally occurring biologically active compounds and building blocks of advanced materials. A one-pot, three-step sustainable synthesis in water was developed starting directly from HMF. The reduction of HMF led to 2,5-bis(hydroxymethyl)furan (BHMF), which could be readily involved in the Diels-Alder cycloaddition reaction with HMF-derived maleimide, followed by hydrogenation of the double bond. The described transformation was diastereoselective and proceeded with a good overall yield. The applicability of the chosen approach for the synthesis of analogous structures containing amine functionality on the side chain was demonstrated. To produce the target compounds, only platform chemicals were used with carbohydrate biomass as the single carbon source.

Dynamic Behavior of Metal Nanoparticles in Pd/C and Pt/C Catalytic Systems under Microwave and Conventional Heating

Metal on carbon catalysts (M/C) are ubiquitously used in modern research and industry to carry out a variety of chemical transformations. Stable metal-support frameworks and inertness of the carbon materials are usually taken for granted in these very useful catalytic systems. Initially, the present study was aimed to increase the efficiency of Pd/C and Pt/C catalytic systems under microwave and conventional heating. Interestingly, a dynamic behavior of the metal nanoparticles was revealed, and a series of carbon support transformations occurred during the thermal treatments of the catalysts. Microwave and thermal heating of the M/C catalysts resulted in substantial transformations of the carbon supports via the formation of pits, trenches, nanofibers and nanowalls. Detailed studies with field-emission scanning electron microscopy was carried out involving statistical averaging over large surface areas. The effects of the dynamic behaviors of the supported metal particles on the catalytic activities of the synthetically useful Mizoroki-Heck and Suzuki-Miyaura reactions were demonstrated. Revealed dynamic behavior and modification of the carbon support due to microwave treatment were observed in a number of M/C systems (M = Pd, Pt, Ni, Co, Сu, Fe and Au).

A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki–Heck Reaction

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal–ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal–NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki–Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M–C or M–H bonds followed by C–NHC or H–NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems.

Toxicity of Metal Compounds: Knowledge and Myths

Organometallic reagents and metal catalysts are used ubiquitously in academia and industry. Not surprisingly, the biological activity and environmental danger of metal compounds have become topics of outstanding importance. In spite of the rapid development of toxicology during the last decades, several common historically established "beliefs" are still frequently circulating in the organometallic community. In this Tutorial, we discuss existing opinions concerning (1) possibilities of toxicity measurements, (2) high toxicities of heavy-metal compounds, (3) correlation between the structure of a metal compound and its toxicity, (4) biological effect of direct/indirect contacts with metal compounds, and (5) dangers of metal nanoparticles. Basic concepts of toxicity studies and known data are described in the Tutorial step by step upon discussion of these issues. The main goal of this Tutorial is to demonstrate that the toxicity of a metal cannot be regarded as a constant property, since it depends on the oxidation state, ligands, solubility, morphology of particles, properties of the environment, and several other factors. As far as such chemically labile species as metal compounds are concerned, the nature of biological effects should not be assumed or taken for granted; indeed, reliable conclusions cannot be made without dedicated measurements.

Investigation of Cytotoxic Activity of Mitoxantrone at the Individual Cell Level by Using Ionic-Liquid-Tag-Enhanced Mass Spectrometry

A novel mitoxantrone conjugate was synthesized by coupling mitoxantrone with ionic liquid tags, and cytotoxic behavior of the designed conjugate was studied in normal and cancer cell lines. The synthesized mitoxantrone conjugate was oil at physiological temperatures and demonstrated high aqueous solubility. Sensitivity of electrospray ionization mass spectrometry (ESI-MS) to the mitoxantrone conjugate was improved by an order of magnitude, in comparison with original mitoxantrone dihydrochloride. The observed ESI-MS signals were shifted to a "clearer" lower-mass region of the spectrum, which allowed investigation of the drug at the level of individual cells. The ionic liquid tags proposed in the present work consist of an easily available imidazolium salt residue and show a number of key advantages from the points of view of drug conjugate synthesis, drug delivery and analytic detection.

Substrate-Selective C−H Functionalization for the Preparation of Organosulfur Compounds from Crude Oil-Derived Components

The direct utilization of a natural feedstock in organic synthesis is an utmost challenge because the selective production of one product from a mixture of starting materials requires unprecedented substrate selectivity. In the present study, a simple and convenient procedure is evaluated for the substrate-selective alkenylation of a single component in a mixture of organosulfur compounds. Pd-catalyzed alkenylation of two-, three-, four-, and five-component mixtures of crude oil-derived sulfur species led to the exclusive C−H functionalization of only one compound. The observed remarkable substrate selectivity opens new opportunities for sustainable organic synthesis.

Acetylene-functionalized platform chemicals were synthesized for the first time based on biomass-derived 5-hydrohymethylfurfural (HMF). Demanded mono- and bis-ethynylfurans were obtained in high yields (89-99%). Plausible application of these products in the synthesis of smart organic conjugated materials and pharmaceuticals was addressed in a series of transformations. Conjugated polyacetylenic polymers with morphology control have been prepared with the incorporation of the HMF core.

Plant Biomass Conversion to Furan Derivatives and Sustainable Access to the New Generation of Polymers, Functional Materials and Fuels

5-Hydroxymethylfurfural (HMF) is an important versatile reagent, a so-called platform chemical, that can be produced from plant biomass compounds: hexose carbohydrates and lignocellulose. In the near future, HMF and its derivatives could become an alternative feedstock for the chemical industry and replace, to a great extent, non-renewable sources of hydrocarbons (oil, natural gas and coal). This review analyzes recent advances in the synthesis of HMF from plant feedstocks and considers the prospects for the use of HMF in the production of monomers and polymers, porous carbon materials, engine fuels, solvents, pharmaceuticals, pesticides and chemicals. The most important HMF derivatives considered in the review include 2,5-furandicarboxylic acid, 2,5-diformylfuran, 2,5-bis(hydroxymethyl)furan, 2,5-bis(aminomethyl)furan, 2,5-dimethylfuran, 2,5-dimethyltetrahydrofuran, 2,5-bis(methoxymethyl)furan, and 5-ethoxymethylfurfural. In the nearest future, a significant extension of the HMF application is expected, and this platform chemical may be considered a major source of carbon and hydrogen for the chemistry of the 21st century.

Which Metals are Green for Catalysis? Comparison of the Toxicities of Ni, Cu, Fe, Pd, Pt, Rh, and Au Salts

Environmental profiles for the selected metals were compiled on the basis of available data on their biological activities. Analysis of the profiles suggests that the concept of toxic heavy metals and safe nontoxic alternatives based on lighter metals should be re-evaluated. Comparison of the toxicological data indicates that palladium, platinum, and gold compounds, often considered heavy and toxic, may in fact be not so dangerous, whereas complexes of nickel and copper, typically assumed to be green and sustainable alternatives, may possess significant toxicities, which is also greatly affected by the solubility in water and biological fluids. It appears that the development of new catalysts and novel applications should not rely on the existing assumptions concerning toxicity/nontoxicity. Overall, the available experimental data seem insufficient for accurate evaluation of biological activity of these metals and its modulation by the ligands. Without dedicated experimental measurements for particular metal/ligand frameworks, toxicity should not be used as a "selling point" when describing new catalysts.

Critical Influence of 5-HMF Aging and Decomposition on the Utility of Biomass Conversion in Organic Synthesis

Spectral studies revealed the presence of a specific arrangement of 5-hydroxymethylfurfural (5-HMF) molecules in solution as a result of a hydrogen–bonding network, and this arrangement readily facilitates the aging of 5-HMF. Deterioration of the quality of this platform chemical limits its practical applications, especially in synthesis/pharma areas. The model drug
Ranitidine (Zantac®) was synthesized with only 15 % yield starting from 5-HMF which was isolated and stored as an oil after a biomass conversion process. In contrast, a much higher yield of 65 % was obtained by using 5-HMF isolated in crystalline state from an optimized biomass conversion process. The molecular mechanisms responsible for 5-HMF decomposition in solution were established by NMR and ESI-MS studies. A highly selective synthesis of a 5-HMF derivative from glucose was achieved using a protecting group at O(6) position.

Direct Observation of Self-Organized Water-Containing Structures in the Liquid Phase and Their Influence on 5-(Hydroxymethyl)furfural Formation in Ionic Liquids

Water-containing organic solutions are widespread reaction media in organic synthesis and catalysis. This type of liquid multicomponent system has a number of unique properties due to the tendency for water to self-organize in mixtures with other liquids. In spite of key importance, the characterization of these water domains is a challenging task due to their soft and dynamic nature. In the present study, morphology and dynamics of μm-scale and nm-scale water-containing compartments in ionic liquids were directly observed by electron microscopy. A variety of morphologies, including isolated droplets, dense structures, aggregates and 2D meshwork, have been experimentally detected and studied. Using the developed method, the impact of water on the acid‑catalyzed biomass conversion reaction was studied at the microscopic level. The process that produced nanostructured domains in solution led to better yields and higher selectivities compared with reactions involving the bulk system.

Visible Light Mediated Metal-free Thiol–yne Click Reaction

The carbon-sulfur bond formation reaction is of paramount importance for functionalized materials design, as well as for biochemical applications. The use of expensive metal-based catalysts and the consequent contamination with trace metal impurities are challenging drawbacks of the existing methodologies. Here, we describe the first environmentally friendly metal-free photoredox pathway to the thiol–yne click reaction. Using Eosin Y as a cheap and readily available catalyst, C-S coupling products were obtained in high yields (up to 91%) and excellent selectivity (up to 60:1). A 3D-printed photoreactor was developed to create arrays of parallel reactions with temperature stabilization to improve the performance of the catalytic system.

Nature of the Copper-Oxide-Mediated C–S Cross-Coupling Reaction: Leaching of Catalytically Active Species from the Metal Oxide Surface

Copper-oxide-catalyzed cross-coupling reaction is a well-known strategy in heterogeneous catalysis. A large number of applications have been developed, and catalytic cycles have been proposed based on the involvement of the copper oxide surface. In the present work, we have demonstrated that copper(I) and copper(II) oxides served as precursors in the coupling reaction between thiols and aryl halides, while catalytically active species were formed upon unusual leaching from the oxide surface. A powerful cryo-SEM technique has been utilized to characterize the solution-state catalytic system by electron microscopy. A series of different experimental methods were used to reveal the key role of copper thiolate intermediates in the studied catalytic reaction. The present study shows an example of leaching from a metal oxide surface, where the leaching process involved the formation of a metal thiolate and the release of water. A new synthetic approach was developed, and many functionalized sulfides were synthesized with yields of up to 96%, using the copper thiolate catalyst. The study suggests that metal oxides may not act as an innocent material under reaction conditions; rather, they may represent a source of reactive species for solution-state homogeneous catalysis.

Synthesis of HIV-1 capsid protein assembly inhibitor (CAP-1) and its analogues based on a biomass approach

A biomass-derived platform chemical was utilized to access a demanded pharmaceutical substance with anti-HIV activity (HIV, human immunodeficiency virus) and a variety of structural analogues. Step economy in the synthesis of the drug core (single stage from cellulose) is studied including flexible variability of four structural units. The first synthesis and X-ray structure of the inhibitor of HIV-1 capsid protein assembly (CAP-1) is described.

Efficient Metal-Free Pathway to Vinyl Thioesters with Calcium Carbide as the Acetylene Source

Chemical reactions involving high-pressure acetylene are not easily performed in a standard laboratory setup. The risk of explosion and technical difficulties drastically complicate the equipment and greatly increase the cost. In this study, we propose the replacement of acetylene with calcium carbide, which was successfully utilized to synthesize practically useful vinyl thioesters in accordance with a simple and environmentally benign procedure. The reaction proceeded under mild conditions using a standard laboratory setup. The optimized reaction conditions allowed the selective synthesis of the vinyl thioesters in high yields, and the reaction conditions can be scaled up to synthesize grams of sulfides from inexpensive starting materials.

Calcium Carbide: A Unique Reagent for Organic Synthesis and Nanotechnology

Acetylene, HC≡CH, is one of the primary building blocks in synthetic organic and industrial chemistry. Several highly valuable processes have been developed based on this simplest alkyne and the development of acetylene chemistry has had a paramount impact on chemical science over the last few decades. However, in spite of numerous useful possible reactions, the application of gaseous acetylene in everyday research practice is rather limited. Moreover, the practical implementation of high-pressure acetylene chemistry can be very challenging, owing to the risk of explosion and the requirement for complex equipment; special safety precautions need to be taken to store and handle acetylene under high pressure, which limit its routine use in a standard laboratory setup. Amazingly, recent studies have revealed that calcium carbide, CaC2, can be used as an easy-to-handle and efficient source of acetylene for in situ chemical transformations. Thus, calcium carbide is a stable and inexpensive acetylene precursor that is available on the ton scale and it can be handled with standard laboratory equipment. The application of calcium carbide in organic synthesis will bring a new dimension to the powerful acetylene chemistry.

Shielding the Chemical Reactivity Using Graphene Layers for Controlling the Surface Properties of Carbon Materials

Graphene can efficiently shield chemical interactions and gradually decrease the binding to reactive defect areas. In the present study, we have used the observed graphene shielding effect to control the reactivity patterns on the carbon surface. The experimental findings show that a surface coating with a tiny carbon layer of 1–2 nm thickness is sufficient to shield the defect-mediated reactivity and create a surface with uniform binding ability. The shielding effect was directly observed using a combination of microscopy techniques and evaluated with computational modeling. The theoretical calculations indicate that a few graphene layers can drastically reduce the binding energy of the metal centers to the surface defects by 40–50 kcal mol
−1. The construction of large carbon areas with controlled surface reactivity is extremely difficult, which is a key limitation in many practical applications. Indeed, the developed approach provides a flexible and simple tool to change the reactivity patterns on large surface areas within a few minutes.

Catalysis to Build Molecular Complexity with Atomic Precision

Editorial introduction to the Special Issue. The smaller, the better: Catalysis takes many forms and has a vast number of applications. Be it heterogeneous or homogeneous, organic, transition-metal or biocatalysis, the many facets of the discipline enable efficient synthetic routes and open up new avenues to previously inaccessible compounds. This special issue is about the catalysis and transformation of complex molecules.

Alkynes as a versatile platform for construction of chemical molecular complexity and realization of molecular 3D printing

The current level of scientific and technological development requires the formation of general tools and techniques. One of the most versatile technologies is 3D printing, which allows fast and efficient creation of materials and biological objects of desired shape and composition. Today, methods have been developed for 3D printing of macro- and nano-sized objects and for production of films and deposited materials with molecular precision but the most promising technology is printing at the molecular level (molecular 3D printing) for the purpose of direct construction of molecular complexity. This process is currently at the initial stage concerning selection of simple molecules to be used as building blocks possessing flexibility, availability and ease of modification. In this review, we examine the possible versatile synthons suitable for preparation of the main types of organic compounds using molecular 3D printing. The surveyed data strongly indicate that alkyne molecules may be used as a building material in a molecular 3D printer working on hydrocarbons.

Selective Synthesis of 2,5-Diformylfuran by Sustainable4-acetamido-TEMPO/Halogen Mediated Electrooxidation of 5-Hydroxymethylfurfural

A new method was developed for the selective gram-scale synthesis of 2,5-diformylfuran (DFF), which is an important chemical with a high application potential, via oxidation of biomass-derived 5-hydroxylmethylfurfural (HMF) catalyzed by 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-AcNH-TEMPO) in a two-phase system consisting of a methylene chloride and aqueous solution containing sodium hydrogen carbonate and potassium iodide. The key feature of this method is the generation of the I2 (co-)oxidant by anodic oxidation of iodide anions during pulse electrolysis. In addition, the electrolyte can be successfully recycled five times while maintaining a 62-65% yield of DFF. This novel method provides sustainable pathway for waste-free production of DFF without the use of metal catalysts and expensive oxidants. An advantage of electrooxidation is utilized in the preparation of demanding chemical.

Plausible role of nanoparticle contamination in the synthesis and properties of organic electronic materials

Traceless transition metal catalysis (Pd, Ni, Cu, etc.) is very difficult to achieve. Metal contamination in the synthesized products is unavoidable and the most important questions are: How to control metal impurities? What amount of metal impurities can be tolerated? What is the influence of metal impurities? In this brief review, the plausible origins of nanoparticle contamination are discussed in the framework of catalytic synthesis of organic electronic materials. Key factors responsible for increasing the probability of contamination are considered from the point of view of catalytic reaction mechanisms. The purity of the catalyst may greatly affect the molecular weight of a polymer, reaction yield, selectivity and several other parameters. Metal contamination in the final polymeric products may induce some changes in the electric conductivity, charge transport properties, photovoltaic performance and other important parameters.

Analysis of 3D Printing Possibilities for the Development of Practical Applications in Synthetic Organic Chemistry

The possibility of rapid manufacturing of customized chemical labware and reactionware by three-dimensional (3D) printing is discussed. The advantages and disadvantages of this approach to the design of chemical equipment from different engineering plastics were demonstrated and the suitability of some materials for chemical applications was estimated: PP > PLA > > ABS > PETG (PP is polypropylene, PLA is polylactide, ABS is acrylonitrile butadiene styrene, and PETG is polyethylene terephthalate glycol). The procedure described is a powerful tool for the production of both typical and unique chemical labware; to date, the fused deposition modeling (FDM) method is already available for the everyday use in chemical laboratories. The examples of successful application of 3D-printed products were demonstrated: solvent resistance and impermeability were assessed, as well as Pd(OAc)2-catalyzed cross-coupling between p-bromotoluene and phenylboronic acid and Ni(acac)2-catalyzed hydrothiolation of alkyne with thiophenol were performed.

Gaining insight into Pd/C catalytic systems aimed at locating reactive centers on carbon surfaces, revealing their properties and estimating the number of reactive centers presents a challenging problem. In the present study state-of-the-art experimental techniques involving ultra high resolution SEM/STEM microscopy (1 Å resolution), high brilliance X-ray absorption spectroscopy and theoretical calculations on truly nanoscale systems were utilized to reveal the role of carbon centers in the formation and nature of Pd/C catalytic materials. Generation of Pd clusters in solution from the easily available Pd
2dba3 precursor and the unique reactivity of the Pd clusters opened an excellent opportunity to develop an efficient procedure for the imaging of a carbon surface. Defect sites and reactivity centers of a carbon surface were mapped in three-dimensional space with high resolution and excellent contrast using a user-friendly nanoscale imaging procedure. The proposed imaging approach takes advantage of the specific interactions of reactive carbon centers with Pd clusters, which allows spatial information about chemical reactivity across the Pd/C system to be obtained using a microscopy technique. Mapping the reactivity centers with Pd markers provided unique information about the reactivity of the graphene layers and showed that >2000 reactive centers can be located per 1 μm2 of the surface area of the carbon material. A computational study at a PBE-D3-GPW level differentiated the relative affinity of the Pd2 species to the reactive centers of graphene. These findings emphasized the spatial complexity of the carbon material at the nanoscale and indicated the importance of the surface defect nature, which exhibited substantial gradients and variations across the surface area. The findings show the crucial role of the structure of the carbon support, which governs the formation of Pd/C systems and their catalytic activity.

Nickel: The "Spirited Horse" of Transition Metal Catalysis

In recent years, the emergence of nickel catalysis and the development of many remarkable synthetic applications have been observed. The key advantages of nickel catalysts include: a) efficient catalysis and the ability to initiate transformations involving usually unreactive substrates; b) the accessibility of Ni0/NiI/NiII/NiIII oxidation states and radical pathways; c) new reactivity patterns beyond the traditional framework of metal catalysts; d) the facile activation of unsaturated molecules and a variety of transformations involving multiple bonds; and e) opportunities in photocatalytic applications and dual photocatalysis. The present viewpoint briefly summarizes the fundamental aspects of nickel chemistry and highlights promising directions of catalyst development.

Pd-NHC Catalytic System for the Efficient Atom-Economic Synthesis of Vinyl Sulfides from Tertiary, Secondary, or Primary Thiols

Vinyl sulfides represent an important class of compounds in organic chemistry and materials science. Atom-economic addition of thiols to the triple bond of alkynes provides an excellent opportunity for environmentally friendly processes. We have found that well-known and readily available Pd-NHC complex (IMes)Pd(acac)Cl is an efficient catalyst for alkyne hydrothiolation. The reported technique provides a general one-pot approach for the selective preparation of Markovnikov-type vinyl sulfides starting from tertiary, secondary, or primary aliphatic thiols, as well as benzylic and aromatic thiols. In all the studied cases, the products were formed in excellent selectivity and good yields.

Three different types of drug delivery platforms based on imidazolium ionic liquids (ILs) were synthesized in high preparative yields, namely, the models involving (i) ionic binding of drug and IL; (ii) covalent binding of drug and IL; and (iii) dual binding using both ionic and covalent approaches. Seven ionic liquids containing salicylic acid (SA-ILs) in the cation or/and in the anion were prepared, and their cytotoxicity toward the human cell lines CaCo-2 (colorectal adenocarcinoma) and 3215 LS (normal fibroblasts) was evaluated. Cytotoxicity of SA-ILs was significantly higher than that of conventional imidazolium-based ILs and was comparable to the pure salicylic acid. It is important to note that the obtained SA-ILs dissolved in water more readily than salicylic acid, suggesting benefits of possible usage of traditional nonsoluble active pharmaceutical ingredients in an ionic liquid form.

An Unexpected Increase of Toxicity of Amino Acid-Containing Ionic Liquids

Functionalization of ionic liquids (ILs) with natural amino acids is usually considered as a convenient approach to decrease their toxicity and find new areas of chemical application as sustainable solvents, reagents or catalysts. In the present study, the cytotoxicity of several amino acid-containing ionic liquids (AAILs) with amino acid-based cations and anions was studied towards NIH/3T3 and CaCo-2 cell cultures and compared with the toxicity of conventional imidazolium-based ILs. The presence of an amino acid in the anion did not lead to a significant decrease in toxicity, whereas in the cation it unexpectedly increased the toxicity, as compared with conventional ILs. Exposure to 1-butyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium glycinate induced apoptosis in NIH/3T3 cells. The present study gives new insights into biological effects of AAILs and shows that an amino acid residue may make ILs more biologically active. Special attention should be paid to the plausible synergetic effect of a combination of ILs with natural biologically active molecules. The results suggest possible medical application of AAILs rather than involvement as a green and sustainable tool to carry out chemical reactions.

Molecular Extraction of Peptides in Ionic Liquid Systems

The extraction of peptides was studied in a two-phase ionic liquid (IL)/organic solvent system, which displayed outstanding chain length sensitivity (dipeptide vs tripeptide) and separation ability, even for structurally similar peptides (divaline vs dialanine). The extraction process could be performed under substoichiometric conditions; an IL-to-peptide ratio as low as 3:1 led to a high extraction selectivity of divaline/dialanine = 6. For practical applications, two systems were developed for the extraction of peptides from ILs under heterogeneous and homogeneous conditions, with selectivities of 6 and 3.5, respectively. The developed system has shown excellent recycling properties and was reused several times without any visible changes in the selectivity and extraction efficiency. A nuclear magnetic resonance (NMR) experiment with molecular-level spatial resolution was successfully performed to study the mechanism of the extraction process and to visualize the two-phase system.

Combined experimental and theoretical studies revealed a complex mechanistic picture in which the carboxylic group-assisted proton transfer from acetic acid to an alkyne molecule is the key step in the unique gold-mediated alkyne transformation that leads to the formation of
gem-disubstituted vinyl gold complexes. The structures of the complexes were unambiguously established using NMR spectroscopy (in solution) and X-ray diffraction (in the solid state). ESI-MS study of the reaction mixture revealed multiple gold-containing complexes and clusters. Investigation of the MS2 fragmentation patterns of the selected ions suggested the involvement of gold acetylides in the transformation. Further treatment of the complexes with protic acid led to the discovery of a novel route for the gold-mediated alkyne hydrothiolation.

Metal complexes with N-heterocyclic carbene ligands (NHC) are ubiquitously used in catalysis, where the stability of the metal–ligand framework is a key issue. Our study shows that Ni-NHC complexes may undergo facile decomposition due to the presence of water in organic solvents (hydrolysis). The ability to hydrolyze Ni(NHC)2X2 complexes decreases in the order of NHC = 1,2,4-triazolium > benzimidazolium ≈ imidazolium. Depending on the ligand and substituents, the half reaction time of the complex decomposition may change from several minutes to hours. The nature of the halogen is also an important factor, and the ability for decomposition of the studied complexes decreases in the order of Cl > Br > I. NMR and MS monitoring revealed that Ni-NHC complexes in the presence of water undergo hydrolysis with Ni–Ccarbene bond cleavage, affording the corresponding
N,N′-dialkylated azolium salts and nickel(II) hydroxide. These findings are of great importance for designing efficient and recyclable catalytic systems, because trace water is a common contaminant in routine synthetic applications.

Analysis of Model Pd- and Pt-Containing Contaminants in Aqueous Media Using ESI-MS and the Fragment Partitioning Approach

Ubiquitous usage of Pd- and Pt-containing nanoparticles in automotive catalytic converters is an important potential threat to the environment. The unavoidable release of transition metal species to the environment and their contact with water give rise to the poisoning of ecosystems by heavy metal compounds. Electrospray ionization mass spectrometry and the newly-developed fragment partitioning approach show that a variety of metal species may be formed upon contact of metal salts with water. A series of monometallic complexes, homonuclear clusters and heteronuclear clusters of palladium and platinum were detected and characterized. The study has revealed a critical danger of metal contamination due to easy formation of transition metal clusters, which may be much more toxic than corresponding monometallic complexes.

Computational Study of a Model System of Enzyme-Mediated [4+2] Cycloaddition Reaction

A possible mechanistic pathway related to an enzyme-catalyzed [4+2] cycloaddition reaction was studied by theoretical calculations at density functional (B3LYP, O3LYP, M062X) and semiempirical levels (PM6-DH2, PM6) performed on a model system. The calculations were carried out for the key [4+2] cycloaddition step considering enzyme-catalyzed biosynthesis of Spinosyn A in a model reaction, where a reliable example of a biological Diels-Alder reaction was reported experimentally. In the present study it was demonstrated that the [4+2] cycloaddition reaction may benefit from moving along the energetically balanced reaction coordinate, which enabled the catalytic rate enhancement of the [4+2] cycloaddition pathway involving a single transition state. Modelling of such a system with coordination of three amino acids indicated a reliable decrease of activation energy by ~18.0 kcal/mol as compared to a non-catalytic transformation.

Organic and Hybrid Molecular Systems

The design of functional organic and hybrid molecular systems has shown outstanding recent growth and is a high priority in the development of new technologies and novel functional materials. Recent advancements in the chemical sciences have provided fascinating opportunities to access the most complex molecular architectures ever possible so far. Herein, we discuss the principles of the structural organization of recently studied molecular systems, basic approaches for their assembly, and challenging directions for their practical applications.

How Sensitive and Accurate are Routine NMR and MS Measurements?

The necessary prerequisites to carry out efficient NMR/MS studies and the important points required to avoid inconsistent measurements are discussed. A comparative assessment of the sensitivity and accuracy of NMR, EI-MS and ESI-MS measurements was carried out to evaluate typical laboratory research performance. Accurate NMR measurements are possible in the 10
–1–10–3 m concentration range, with spectral studies still being possible at concentrations of approximately 10–4–10–5 m. EI-MS is more sensitive and can operate at concentrations of 10–6 m, while commonly available ESI-MS can be efficient up to a concentration of 10–18 m.

Microwave irradiation of Ni, Co, Cu, Ag, and Pt metal salts supported on graphite and charcoal revealed a series of carbon surface modification processes that varied depending on the conditions used (inert atmosphere, vacuum, or air) and the nature of metal salt. Carbon materials, routinely used to prepare supported metal catalysts and traditionally considered to be innocent on this stage, were found to actively change under the studied conditions: etching and pitting of the carbon surface by metal particles as well as growth of carbon nanotubes were experimentally observed by FE-SEM analysis. Catalyst preparation under microwave irradiation led to the formation of complex metal/carbon structures with significant changes in carbon morphology. These findings are of great value in developing an understanding of how M/C catalysts form and evolve and will help to design a new generation of efficient and stable catalysts. The energy surfaces of carbon support modification processes were studied with theoretical calculations at the density functional level. The energy surface of the multistage process of carbon nanotube formation from an etched graphene sheet was calculated for various types of carbon centers. These calculations indicated that interconversion of graphene layers and single wall carbon nanotubes is possible when cycloparaphenylene rings act as building units.

Miniaturization of NMR Systems: Desktop Spectrometers, Microcoil Spectroscopy, and "NMR on a Chip" for Chemistry, Biochemistry, and Industry

Toxicity of Ionic Liquids: Eco(cyto)activity as Complicated, but Unavoidable Parameter for Task-Specific Optimization

Rapid progress in the field of ionic liquids in recent decades led to the development of many outstanding energy-conversion processes, catalytic systems, synthetic procedures, and important practical applications. Task-specific optimization emerged as a sharpening stone for the fine-tuning of structure of ionic liquids, which resulted in unprecedented efficiency at the molecular level. Ionic-liquid systems showed promising opportunities in the development of green and sustainable technologies; however, the chemical nature of ionic liquids is not intrinsically green. Many ionic liquids were found to be toxic or even highly toxic towards cells and living organisms. In this Review, we show that biological activity and cytotoxicity of ionic liquids dramatically depend on the nature of a biological system. An ionic liquid may be not toxic for particular cells or organisms, but may demonstrate high toxicity towards another target present in the environment. Thus, a careful selection of biological activity data is a must for the correct assessment of chemical technologies involving ionic liquids. In addition to the direct biological activity (immediate response), several indirect effects and aftereffects are of primary importance. The following principal factors were revealed to modulate toxicity of ionic liquids: i) length of an alkyl chain in the cation; ii) degree of functionalization in the side chain of the cation; iii) anion nature; iv) cation nature; and v) mutual influence of anion and cation.

Unprecedented Control of Selectivity in Ni-Catalyzed Hydrophosphorylation of Alkynes: Efficient Route to Mono- and Bisphosphonates

A unique nickel-based catalytic system was developed where the direction of the hydrophosphorylation reaction can be controlled by varying the catalyst loading. A flexible one-pot access to vinylmonophosphonates and alkylbisphosphonates was demonstrated using simple starting materials in an atom-economic reaction without any specific solvents or ligands. Monitoring of the reaction mechanism with joint NMR and MS studies revealed key information about the reaction intermediates. The synthetic scope of the developed catalytic system was explored and the utility of the synthesized products for the fire protection of cotton materials was demonstrated.

Carboxylate Switch between Hydro- and Carbopalladation Pathways in Regiodivergent Dimerization of Alkynes

Experimental and theoretical investigation of the regiodivergent palladium-catalyzed dimerization of terminal alkynes is presented. Employment of N-heterocyclic carbene-based palladium catalyst in the presence of phosphine ligand allows for highly regio- and stereoselective head-to-head dimerization reaction. Alternatively, addition of carboxylate anion to the reaction mixture triggers selective head-to-tail coupling. Computational studies suggest that reaction proceeds via the hydropalladation pathway favoring head-to-head dimerization under neutral reaction conditions. The origin of the regioselectivity switch can be explained by the dual role of carboxylate anion. Thus, the removal of hydrogen atom by the carboxylate directs reaction from the hydropalladation to the carbopalladation pathway. Additionally, in the presence of the carboxylate anion intermediate, palladium complexes involved in the head-to-tail dimerization display higher stability compared to their analogues for the head-to-head reaction.

Exclusive Selectivity in the One-Pot Formation of C-C and C-Se Bonds Involving Ni-catalyzed Alkynes Hydroselenation: Optimization of the Synthetic Procedure and a Mechanistic Study

A unique Ni-catalyzed transformation is reported for the one-pot highly selective synthesis of previously unknown monoseleno-substituted 1,3-dienes starting from easily available terminal alkynes and benzeneselenol. The combination of a readily available catalyst precursor, Ni(acac)2, and an appropriately tuned phosphine ligand, PPh2Cy, resulted in the exclusive assembly of the s-gauche diene skeleton via the selective formation of C–C and C–Se bonds. The unusual diene products were stable under regular experimental conditions, and the products maintained the s-gauche geometry both in the solid state and in solution, as confirmed by X-ray analysis and NMR spectroscopy. Thorough mechanistic studies using ESI-MS revealed the key Ni-containing species involved in the reaction.

Nanoscale Organization of Ionic Liquids and Their Interaction with Peptides Probed by 13C NMR Spectroscopy

An NMR study of 10
l-alanine- and l-valine-containing peptides was carried out in the native [C2MIM][Cl], [C4MIM][Cl], [C6MIM][Cl], [C4MIM][BF4], [C4MIM][PF6], and [C4Py][BF4] ionic liquid media. A unique high sensitivity of the ionic liquid system to the nature of peptide and ability to tune solvent–solute interactions were observed in contrast to regular organic solvents. The l-valine peptides can be selectively dissolved in [C4MIM][Cl] and [C6MIM][Cl], whereas their solubility in [C2MIM][Cl] and other ionic liquids was dramatically lower. In spite of structural similarity between the amino acids, a distinct behavior was observed for the l-alanine peptides. Solvent–solute interactions with an ionic liquid impose significant changes, and NMR spectroscopy is a useful probe for the molecular-level and nanoscale organization of the studied systems. An even/odd effect of the number of amino acids in the peptide on molecular interactions in ionic liquids was observed. Enhancement of chemical properties of peptides in ionic liquids and application of ionic liquids in the separation of peptides are the areas of practical interest in the studied systems.

Development of New Methods in Modern Selective Organic Synthesis: Preparation of Functionalized Molecules with Atomic Precision

Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

The experimental study of dechlorination activity of a Au/Ag bimetallic system has shown formation of a variety of chlorinated bimetallic Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It is the formation of the Au/Ag cluster species that mediated C–Cl bond breakage, since neither Au nor Ag species alone exhibited a comparable activity. The nature of the products and the mechanism of dechlorination were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations at the M06/6-311G(d)&SDD level of theory. It was revealed that formation of bimetallic clusters facilitated dechlorination activity due to the thermodynamic factor: C–Cl bond breakage by metal clusters was thermodynamically favored and resulted in the formation of chlorinated bimetallic species. An appropriate Au:Ag ratio for an efficient hydrodechlorination process was determined in a joint experimental and theoretical study carried out in the present work. This mechanistic finding was followed by synthesis of molecular bimetallic clusters, which were successfully involved in the hydrodechlorination of CCl
4 as a low molecular weight environment pollutant and in the dechlorination of dichlorodiphenyltrichloroethane (DDT) as an eco-toxic insecticide. High activity of the designed bimetallic system made it possible to carry out a dechlorination process under mild conditions at room temperature.

Modulation of Chemical Interactions Across Graphene Layers and Metastable Domains in Carbon Materials

Attachment of palladium clusters to carbon surface was investigated by SEM and STEM methods that have suggested plausible modification of chemical interactions across graphene layers; the fact can explain mismatches between domain structures and alignment patterns of palladium nanoparticles observed experimentally by the electron microscopy.

Exceptional Behavior of Ni2O2 Species Revealed by ESI-MS and MS/ MS Studies in Solution. Application of Superatomic Core To Facilitate New Chemical Transformations

Acetonitrile solutions of nickel(II) acetylacetonate, which is ubiquitously used in different fields of organometallic chemistry and catalysis, were investigated by means of electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The detected Ni2(acac)3+ ion with the binuclear Ni2O2 core underwent a wide range of reactions after collision-induced dissociation, leading to a variety of products. Activation of C–H, C–C, and C–O bonds was observed involving the binuclear nickel complex. In sharp contrast, similar ions involving mononuclear and trinuclear nickel species did not show such exceptional behavior. The findings may open a fascinating direction in the field of superatoms to develop new chemical transformations for organometallic chemistry and catalysis. The higher relative stability of binuclear species was also observed in ESI mass spectra of copper and vanadyl complexes with acetylacetonate ligands, Cu2(acac)3+ and (VO)2(acac)3+. An important point concerns the purity of the studied solutions, since even a trace level of contaminants has drastically diminished the outcome of the mechanistic studies.

Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl4 Source. Localization of Homogeneous/Heterogeneous System's Interface and Field-Emission Scanning Electron Microscopy Study

Soluble gold precatalysts, aimed for homogeneous catalysis, under certain conditions may form nanoparticles, which dramatically change the mechanism and initiate different chemistry. The present study addresses the question of designing gold catalysts, taking into account possible interconversions and contamination at the homogeneous/heterogeneous system's interface. It was revealed that accurate localization of boundary experimental conditions for formation of molecular gold complexes in solution versus nucleation and growth of gold particles opens new opportunities for well-known gold chemistry. Within the developed concept, a series of practical procedures was created for efficient synthesis of soluble gold complexes with various phosphine ligands (R3P)AuCl (90–99% yield) and for preparation of different types of gold materials. The effect of the ligand on the particles growth in solution has been observed and characterized with high-resolution field-emission scanning electron microscopy (FE-SEM) study. Two unique types of nanostructured gold materials were prepared: hierarchical agglomerates and gold mirror composed of ultrafine smoothly shaped particles.

In situ generated catalysts and preformed catalysts are two practical strategies widely used in cross-coupling methodology that have long been considered to involve the same active species in the catalytic cycle. Recent mechanistic studies have revealed two fundamentally different pictures of catalytic reactions in solution. Preformed catalysts with strongly bound ligands initiate transformations mainly involving single type of metal species. In contrast, in situ generated catalysts give rise to cocktail-type systems with different metal species presented in solution. The role of catalyst precursor, interconversions of catalytic species during reaction, stability and recycling of catalyst, catalysis by autocatalyst exhaust and plausible sources of metal-containing contaminants are the key points discussed in this review.

Self-assembled monolayers (SAMs) of selenium have emerged into a rapidly developing field of nanotechnology with several promising opportunities in materials chemistry and catalysis. Comparison between sulfur-based self-assembled monolayers and newly developed selenium-based monolayers reveal outstanding complimentary features on surface chemistry and highlighted the key role of the headgroup element. Diverse structural properties and reactivity of organosulfur and organoselenium groups on the surface provide flexible frameworks to create new generations of materials and adaptive catalysts with unprecedented selectivity. Important practical utility of adaptive catalytic systems deals with development of sustainable technologies and industrial processes based on natural resources. Independent development of nanotechnology, materials science and catalysis has led to the discovery of common fundamental principles of the surface chemistry of chalcogen compounds.

Recent Advances in Computational Predictions of NMR Parameters for the Structure Elucidation of Carbohydrates: Methods and Limitations

All living systems are comprised of four fundamental classes of macromolecules – nucleic acids, proteins, lipids, and carbohydrates (glycans). Glycans play a unique role of joining three principal hierarchical levels of the living world: (1) the molecular level (pathogenic agents and vaccine recognition by the immune system, metabolic pathways involving saccharides that provide cells with energy, and energy accumulation
via photosynthesis); (2) the nanoscale level (cell membrane mechanics, structural support of biomolecules, and the glycosylation of macromolecules); (3) the microscale and macroscale levels (polymeric materials, such as cellulose, starch, glycogen, and biomass). NMR spectroscopy is the most powerful research approach for getting insight into the solution structure and function of carbohydrates at all hierarchical levels, from monosaccharides to oligo- and polysaccharides. Recent progress in computational procedures has opened up novel opportunities to reveal the structural information available in the NMR spectra of saccharides and to advance our understanding of the corresponding biochemical processes. The ability to predict the molecular geometry and NMR parameters is crucial for the elucidation of carbohydrate structures. In the present paper, we review the major NMR spectrum simulation techniques with regard to chemical shifts, coupling constants, relaxation rates and nuclear Overhauser effect prediction applied to the three levels of glycomics. Outstanding development in the related fields of genomics and proteomics has clearly shown that it is the advancement of research tools (automated spectrum analysis, structure elucidation, synthesis, sequencing and amplification) that drives the large challenges in modern science. Combining NMR spectroscopy and the computational analysis of structural information encoded in the NMR spectra reveals a way to the automated elucidation of the structure of carbohydrates.

Fast and Accurate Computational Modelling of Adsorption on Graphene: a Dispersion Interaction Challenge

Understanding molecular interactions of graphene is a question of key importance to design new materials and catalytic systems for practical usage. Although for small models good accuracy was demonstrated in theoretical analysis with
ab initio and density functional methods, the application to real-size systems with thousands of atoms is currently hardly possible on routine bases due to the high computational cost. In the present study we report that incorporation of dispersion correction led to the principal improvement in the description of graphene systems at a semi-empirical level. The accuracy and the scope of the calculations were explored for a wide range of molecules adsorbed on graphene surfaces (H2, N2, CO, CO2, NH3, CH4, H2O, benzene, naphthalene, coronene, ovalene and cyclohexane). As a challenging parameter, the calculated adsorption energy of aromatic hydrocarbons on graphene Eads = −1.8 ± 0.1 kcal mol−1 (per one carbon atom) at the PM6-DH2 level was in excellent agreement with the experimentally determined value of Eads = −1.7 ± 0.3 kcal mol−1. The dispersion corrected semi-empirical method was found to be a remarkable computational tool suitable for everyday laboratory studies of real-size graphene systems. Significant performance improvement (ca. 103 times faster) and excellent accuracy were found as compared to the ωB97X-D density functional calculations.

An easy and convenient procedure is described for monitoring chemical reactions and characterization of compounds dissolved in ionic liquids using the well-known tandem mass spectrometry (MS/MS) technique. Generation of wastes was avoided by utilizing an easy procedure for analysis of ionic liquid systems without preliminary isolation and purification. The described procedure also decreased the risk of plausible contamination and damage of the ESI-MS hardware and increased sensitivity and accuracy of the measurements. ESI-MS detection in MS/MS mode was shown to be efficient in ionic liquids systems for structural and mechanistic studies, which are rather difficult otherwise. The developed ESI-MS/MS approach was applied to study samples corresponding to peptide systems in ionic liquids and to platform chemical directed biomass conversion in ionic liquids.

A new approach for the catalytic carbon–sulfur bond formation via cross-coupling reaction is reported. For the first time nano-structured nickel organosulfides [Ni(SAr)2]n were used as a source of SAr groups in catalytic cross-coupling reaction. A unique effect of morphology control of the reactivity of SAr groups in cross-coupling reaction was found. Synthesized nano-structured particles were characterized by field-emission scanning electron microscopy and their reactivity was studied by NMR in solution. Cross-coupling reaction with Cu catalyst was shown to proceed in the liquid phase and involve leaching, whereas the reaction with Pd catalyst is more complex and may involve both—homogeneous and heterogeneous pathways.

Dependence of Catalytic Activity of Metal-Containing Particles on Degree of Ordering Rather Than on Size and Shape. Pd and Ni-Catalyzed Carbon-Heteroatom Bond Formation

High selectivity and good yields in the catalytic addition of thiols and selenols to alkynes were observed for Ni and Pd chalcogenide catalyst particles with high degree of ordering, whereas direct correlation with size and shape of the particles was not identified.

Alkyne and Alkene Insertion into Metal-Heteroatom and Metal-Hydrogen Bonds: The Key Stages of Hydrofunctionalization Process

In this chapter we review mechanistic concepts of carbon–heteroatom bond formation involving hydrofunctionalization of double and triple carbon–carbon bonds via migratory insertion pathway. A variety of useful synthetic procedures were developed within the scope of hydrofunctionalization reaction involving transition metal catalysts to change the direction of the addition reaction and to improve the selectivity of the process. Outstanding potential of multiple bonds activation and insertion in the metal complexes is far from being fully explored. The key factors determining insertion pathways into metal–heteroatom vs. metal–hydrogen bonds and the influence on regioselectivity of the insertion remain to be revealed in nearest future.

In the present review we describe the emerging tendency for creating target-oriented analytical approaches designed to solve important chemical tasks by using a combination of analytical tools. The concept is illustrated by selected examples of advances of NMR spectroscopy, mass spectrometry and electron microscopy in the analysis and study of gas-phase, liquid-state and solid-state chemical systems. Comparative description of chemical applications of these analytical methods is presented and discussed. The bibliography includes 359 references.

An unprecedented sustainable procedure was developed to produce functionalized vinyl monomers H2C═C(R)(FG) starting from a mixture of sulfur and selenium compounds as a functional group donor (FG = S or Se). The reaction serves as a model for efficient utilization of natural resources of sulfur feedstock in oil and technological sources of sulfur/selenium. The catalytic system is reported with amazing ability to recognize SH/SeH groups in the mixture and selectively incorporate them into valuable organic products via wastes-free atom-economic reaction with alkynes (HC≡CR). Formation of catalyst active site and the mechanism of the catalytic reaction were revealed by joint experimental and theoretical study. The difference in reactivity of μ1- and μ2-type chalcogen atoms attached to the metal was established and was shown to play the key role in the action of palladium catalyst. An approach to solve a challenging problem of dynamically changed reaction mixture was demonstrated using adaptive tuning of the catalyst. The origins of the adaptive tuning effect were investigated at molecular level and were found to be governed by the nature of metal–chalcogen bond.

Toward the Ideal Catalyst: From Atomic Centers to a "Cocktail" of Catalysts

The current state of the art and perspectives of homogeneous and heterogeneous catalysis are discussed for C–C and C–heteroatom bond formation in organic synthesis. The relationship between catalyst centers represented by a single metal atom and by multiple metal atoms is considered for reactions taking place in solution. The influence of leaching and catalyst evolution in the liquid phase on the activity, selectivity, and stability of the catalyst is highlighted from a mechanistic point of view. Metal nanoparticle and "nanosalt" types of catalysts are compared for constructing new C–C and C–heteroatom bonds.

The mechanistic nature of the conversion of carbohydrates to the sustainable platform chemical 5-hydroxymethylfurfural (5-HMF) was revealed at the molecular level. A detailed study of the key sugar units involved in the biomass conversion process has shown that the simple dissolution of fructose in the ionic liquid 1-butyl-3-methylimidazolium chloride significantly changes the anomeric composition and favors the formation of the open fructoketose form. A special NMR approach was developed for the determination of molecular structures and monitoring of chemical reactions directly in ionic liquids. The transformation of glucose to 5-HMF has been followed in situ through the detection of intermediate species. A new environmentally benign, easily available, metal-free promoter with a dual functionality (B2O3) was developed for carbohydrate conversion to 5-HMF.

Pd2(dba)3 as a Precursor of Soluble Metal Complexes and Nanoparticles: Determination of Palladium Active Species for Catalysis and Synthesis

Tris(dibenzylideneacetone)dipalladium (Pd2(dba)3) is ubiquitously used as a source of soluble Pd species for catalysis and as a precursor in the synthesis of more complex Pd structures. In spite of the massive usage of this convenient Pd complex, its nature in solution has not been revealed in detail and the applications rely on the assumed state and purity of the compound. In the present study we have developed a convenient NMR procedure to reveal the nature of Pd2(dba)3 and to determine the purity of the complex. Surprisingly, it was found that commercially available samples of Pd2(dba)3 may readily contain up to 40% of Pd nanoparticles in a wide range of sizes (10–200 nm). The study has shown that the routinely accepted practice of utilization of Pd2(dba)3 without analysis of the purity (both commercially available and prepared by common procedures) can introduce significant errors in the estimation of catalyst efficiency and lead to incorrect values of TON, TOF, and reported mol % values in the catalytic procedures. The presence of Pd nanoparticles in the catalyst precursor provides an opportunity for heterogeneous catalytic systems of different nature to be directly accessible from Pd2(dba)3. In the present study we report a modified procedure for the synthesis of Pd2(dba)3CHCl3 with 99% purity.

Linear Encoding of Functional Groups in the Synthesis of Heterocyclic Compounds: Cycloaddition of Enyne and Alkyne Units

A family of novel [4+2]-cycloaddition reactions is discussed to carry out efficient preparation of poly-substituted heterocyclic compounds in a single-step starting with linear precursors. High selectivity of the intramolecular transformation and pre-defined position
of substituents in the product were governed by linear encoding in the structure of starting
reagents. The designed reactions utilized green chemistry potential of cycloaddition approach
and provided a convenient synthetic route to cyclopentapyridines, indoles,isoindoles,
indolizines, isophosphindoles, benzofurans, benzothiophenes, benzoselenophenes (and
corresponding dihydro derivatives).

A general highly regio- and stereoselective palladium-catalyzed head-to-head dimerization reaction of terminal acetylenes is presented. This methodology allows for the efficient synthesis of a variety of 1,4-enynes as single
E stereoisomers. Computational studies reveal that this dimerization reaction proceeds via the hydropalladation pathway.

Unusual Control of Reaction Selectivity via a Subtle Change in the Ligand: Proof of Concept and Application in Pd-Catalyzed C-P Bond Formation

A new concept for the design of ligands for transition-metal-catalyzed reactions is described. It was shown that the steric effect of triarylphosphanes upon coordination to a metal center can be controlled by switching between unrestricted and restricted rotation modes. The ligands studied were intrinsically tuned to possess characteristic signals in the
1H, 13C, 31P NMR and electrospray ionization mass spectrometry (ESI-MS), thus allowing mechanistic studies to be easily carried out. The efficiency of the developed method was demonstrated in a study on the mechanistic pathways of Pd-catalyzed hydrophosphorylation of alkynes. The catalytic cycle was explored step-by-step by using ESI-MS and NMR methods. Several Pd species were detected under catalytic conditions and the nature of the intermediate metal complexes were evaluated. The process responsible for capturing the Pd catalyst in the inactive resting state and the routes leading to catalyst decomposition were identified and described. For the first time, the catalytic reaction mechanism of hydrophosphorylation of alkynes was revealed at a molecular level, which led to the design of a novel practical procedure for Pd-mediated C–P bond formation. A new Pd/P[(MeO)nC6H5–n]3 catalytic system was proposed with the outstanding ability to control reaction selectivity simply by adjusting the methoxy substituents in the phosphane ligand.

PEG as an Alternative Reaction Medium in Metal-Mediated Transformations

Poly(ethylene glycol)s (PEGs) are an interesting environment-friendly alternative to classical solvents. Their combination with metals and metallic salts provides powerful reaction systems for a wide variety of transformations. This study presents an overview of the various reactions developed in PEG together with a metallic species. The influence of PEG on the reaction course, the stabilizing effects of the polymer on the metals and the recycling possibility are reported for the various metallic elements of the periodic table.

A new efficient approach was developed for the synthesis of aromatic and heteroaromatic compounds based on [4 + 2] cycloaddition of unsubstituted and heteroatom-substituted alkyne and enyne units. The developed approach provides a practical Green chemical route to several types of important bicyclic products (indane, cyclopentapyridines, indole, isoindole, indolizine, isophosphindole, benzofuran, benzothiophene, benzoselenophene and corresponding dihydro derivatives) starting from simple linear compounds. The mechanism of the reactions was revealed by theoretical calculations using different methods, including CCSD(T) and MP4(SDTQ) for energy calculations and B3LYP, M052X, B3PW91, BLYP and MP2 levels for evaluation of molecular structures.

NMR Analysis of Chiral Alcohols and Amines: Development of Environmentally Benign "In Tube" Procedure with High Efficiency and Improved Detection Limit

A fast and efficient approach was developed for the NMR analysis of chiral alcohols and amines using readily available enantiopure MPA (α-methoxy-α-phenylacetic acid) and MTPA (α-methoxy-α-trifluoromethylphenylacetic acid) as chiral derivatizing agents. The procedure requires less than 5 min (including sample preparation time) for analysis using routine NMR hardware and allows accurate measurements for
<0.01 mg of the sample of chiral compounds. Direct "in tube" analysis can be performed with high efficiency to determine enantiomeric purity and absolute configuration, as well as to monitor reactions in asymmetric synthesis and catalysis. The developed procedure is superior in terms of waste-free analysis of chiral compounds for environmentally benign applications.

Non-catalytic and catalytic addition reactions were compared in this review, with a special attention paid to the factors controlling selectivity and yields. The scope and limitations of Ni, Pd, Pt, Rh and Au catalysts for the formation of C-S, C-Se and C-Te bonds were discussed with an impact of development of Green chemical methods.

Alkyne Insertion into the M-P and M-H Bonds (M = Pd, Ni, Pt, and Rh): A Theoretical Mechanistic Study of the C-P and C-H Bond-Formation Steps

In hydrogen-metal-phosphorus (HMP) transition metal complexes (proposed as intermediates of HP bond addition to alkynes in the catalytic hydrophosphorylation, hydrophosphinylation, and hydrophospination reactions), alkyne insertion into the metal-hydrogen bond was found much more facile compared to alkyne insertion into the metal-phosphorus bond. The conclusion was verified for different metals (Pd, Ni, Pt, and Rh), ligands, and phosphorus groups at various theory levels (B3LYP, B3PW91, BLYP, MP2, and ONIOM). The relative reactivity of the metal complexes in the reaction with alkynes was estimated and decreased in the order of Ni>Pd>Rh>Pt. A trend in relative reactivity was established for various types of phosphorus groups: PR2>P(O)R2>P(O)(OR)2, which showed a decrease in rate upon increasing the number of the oxygen atoms attached to the phosphorus center.

Preparation of Metal "Nanosalts" and Their Application in Catalysis: Heterogeneous and Homogeneous Pathways

A novel type of nanoparticles have been designed based on self-organization of the metal centers with organic functional groups. Size- and shape-controlled synthetic procedures were developed to prepare nanostructured Pd and Ni particles in high yields from easily available precursors. The presence of the non-metallic functional groups in the particle's core forced the metal centers to adopt a divalent oxidation state bearing polar chemical bonds ("nanosalt"). The Pd and Ni particles were excellent catalysts to accomplish a highly selective synthetic route to vinyl chalcogenides. The mechanisms of the catalytic reactions
via the heterogeneous and homogeneous pathways were revealed and studied in detail.

An automated algorithm for fast quantum chemical modeling of NMR spectra within the framework of the density functional theory was developed. High accuracy of calculations of NMR parameters achieved for various classes of organic compounds including heterocyclic compounds, carbohydrates, steroids, and peptides is comparable with the accuracy of experimental determination. The efficiency of computing the NMR chemical shifts using the high-performance PBE/PRIRODA method was demonstrated.

NMR Approach for the Identification of Dinuclear and Mononuclear Complexes: The First Detection of [Pd(SPh)2(PPh3)2] and [Pd2(SPh)4(PPh3)2] - The Intermediate Complexes in the Catalytic Carbon-Sulfur Bond Formation Reaction

In the present study we have analyzed the nature of palladium complexes in the catalytic system for selective carbon–sulfur bond formation
via the addition of S–S and S–H bonds to alkynes. For the first time the mononuclear and dinuclear palladium complexes were clearly detected by DOSY NMR under the catalytic conditions. It was demonstrated that the concentration of these palladium complexes strongly depends on the amount of phosphine ligand available under reaction conditions

The first practical procedure is reported for the synthesis of (E,E)-1,4-diiodobuta-1,3-diene from very simple starting materials (acetylene and I2). A pure crystalline product was obtained in a green chemical procedure utilizing the key advantages of highly selective Pt-catalyzed transformation and 100% atom efficiency of the addition reaction. The Pt catalyst was recovered and re-used in the reaction without a noticeable loss of activity.

The Unique Role of Orientation and Properties of Phosphorus Group in the Alkyne Insertion Step Related to Catalytic Hydrofunctionalization via P-H Bond Addition

The puzzling question of alkyne insertion into PdP and PdH bonds leading to the formation of new PdC, CP, and CH bonds was explored by theoretical calculations at the CCSD(T) and B3LYP levels of theory. The key factors responsible for selectivity of catalytic hydrofunctionalization of alkynes were resolved and studied in details for the models of hydrophosphorylation, hydrophosphinylation, and hydrophospination reactions. In contrast with the generally accepted mechanistic picture, the calculations have shown that several pathways are possible depending on the nature and geometrical arrangement of the phosphorus group. It was found that the product of alkyne insertion into the metal–hydrogen bond should be easily formed under kinetic-control conditions, while the product of alkyne insertion into the metal–phosphorus bond may be formed in certain cases under thermodynamic control. For the first time, the calculations have revealed the role of the oxygen atom in the reactivity of P=P(O)R2 groups and the role of the interactions involving the lone pair of the P=PR2 group in the reagent. The fundamental properties of the PdP, CP, and PH bonds were reported, and the larger bond strength upon increasing the number of oxygen atoms bound to phosphorus (P=PR2, P(O)R2, and P(O)(OR)2) have been shown. The relationship between bond energy, acidity, and reactivity of the studied phosphorus compounds has been determined.

1,4-Diiodo-1,3-dienes: Versatile Reagents in Organic Synthesis

1,4-Diiodo-1,3-dienes are unique reagents in organic synthesis and have been employed in several well-known and recently developed areas of application. Furthermore, these dienes are easily accessible, starting from the alkynes and
iodine, and they have demonstrated high reactivity in cross-coupling reactions, organometallic synthesis, in the preparation of heterocyclic compounds, and several other transformations. The high reactivity of the 1,4-diiodo-1,3-dienes allows for the development of synthetic procedures that use mild conditions (room temperature). The key advantages in assembling complex organic molecules, natural products, and compounds for material science using 1,4-diiodo-1,3-dienes as building blocks include high yields, excellent selectivity, and diverse reactivity in carboncarbon and carbonheteroatom bond formation. This Focus Review describes the scope and application of the 1,4-diiodo-1,3-dienes in organic synthesis as well as summarizes the methods for preparation of the dienes.

First Principles Design of Derivatizing Agent for Direct Determination of Enantiomeric Purity of Chiral Alcohols and Amines by NMR Spectroscopy

77Se NMR offers superior sensing of chirality within the structure of the diastereomers (Δδ up to 6.1 ppm), compared to 13C (Δδ < 1 ppm) and 1H (Δδ < 0.2 ppm). The developed procedure is equally well suitable for determination of the enantiomeric purity of chiral alcohols and amines as pure samples as well as reaction mixtures and crude products.

Ni(acac)2/Phosphine as an Excellent Precursor of Nickel(0) for Catalytic Systems

The coordination of phosphine ligands to nickel acetylacetonate was studied in toluene solution, and the first X-ray structure of the unstable complex
trans-[Ni(acac)2(PMe2Ph)2] has been reported. A convenient procedure was developed to generate Ni(0) species in situ in solution from a Ni(acac)2 precursor, and their application in catalysis was demonstrated. A study of the reaction mechanism has suggested that water may play an important role in the formation of zerovalent nickel species. The nature of the Ni(0) species was confirmed by trapping with Ph2S2, and the structure of the resulting complexes trans-[Ni(SPh)2L2] was established by X-ray analysis for L = PMe2Ph, PMePh2, PBu3.

Two Distinct Mechanisms of Alkyne Insertion into the Metal-Sulfur Bond: Combined Experimental and Theoretical Study and Application in Catalysis

The present study reports the evidence for the multiple carbon–carbon bond insertion into the metal–heteroatom bond via a five-coordinate metal complex. Detailed analysis of the model catalytic reaction of the carbon–sulfur (CS) bond formation unveiled the mechanism of metal-mediated alkyne insertion: a new pathway of CS bond formation without preliminary ligand dissociation was revealed based on experimental and theoretical investigations. According to this pathway alkyne insertion into the metal–sulfur bond led to the formation of intermediate metal complex capable of direct CS reductive elimination. In contrast, an intermediate metal complex formed through alkyne insertion through the traditional pathway involving preliminary ligand dissociation suffered from "improper" geometry configuration, which may block the whole catalytic cycle. A new catalytic system was developed to solve the problem of stereoselective SS bond addition to internal alkynes and a cost-efficient Ni-catalyzed synthetic procedure is reported to furnish formation of target vinyl sulfides with high yields (up to 99 %) and excellent Z/E selectivity (>99:1).

Mechanistic Insight Into Organic and Catalytic Reactions by Joint Studies Using Mass Spectrometry and NMR Spectroscopy

Utilization of NMR spectroscopy and mass spectrometry for joint mechanistic and structural studies is a well-known practice. Several opportunities have appeared in recent years because of new hardware development and design of novel experimental procedures. Recent progress in this area and leading examples of new development, as well as already distinguished techniques, are discussed.

The Comparison of Addition of Molecules Possessing P(V)–H Bond to Alkynes Catalyzed with Pd and Ni Complexes

Main factors have been analyzed necessary for creation of an efficient catalytic system for alkynes hydrophosphorylation based on nickel complexes, and a valid model system was suggested for the comparison with palladium complexes. It has been discovered for the first time that the insertion of an alkyne into the metal-hydrogen bond occurs with a considerably lower activation barrier than into the metal-phosphorus bond, whereas the variation in the reaction energy corresponds in both cases to an exothermic reaction. Under the optimized conditions the transformation catalyzed by nickel complexes does not require acid addition and may proceed even in the absence of a phosphine ligand.

Real Size of Ligands, Reactants and Catalysts: Studies of Structure, Reactivity and Selectivity by ONIOM and Other Hybrid Computational Approaches

The nickel catalyst prepared
in situ from nickel bis(acetylacetonate) [Ni(acac)2] precursor and bis(diphenylphosphino)ethane (DPPE) ligand has shown excellent performance in the hydrophosphorylation of alkynes. Markovnikov-type regioselective addition to terminal alkynes and stereoselective addition to internal alkynes were carried out with high selectivity without an acidic co-catalyst (in contrast to the palladium/acid catalytic system). Various H-phosphonates and alkynes reacted smoothly in the developed catalytic system with up to 99% yield. The mechanisms of catalyst activation and CP bond formation were revealed by experimental (NMR, ESI-MS, X-ray) and theoretical (density functional calculations) studies. Two different pathways of the alkyne insertion in the coordination sphere of the metal are reported for the first time.

Sulfur-Containing Alkenes - A New Class of Chelating Ligands: Synthesis, Coordination to Palladium, and Structure of the Resulting Complexes

Stable 1,2-disulfanylalkene palladium complexes [(RS-CH=CR′-SR)PdCl2] were synthesized in 85–94% yield by reaction of palladium(II) chloride with sulfur-containing ligands RS-CH=C(R′)-SR (analogs of dithiolate ligands). The structure of the complexes was studied by NMR spectroscopy and quantum-chemical methods. The binding energy in palladium complexes with bis(arylsulfanyl)- and bis(alkylsulfanyl)alkenes was estimated (DFT) at 50 and 56 kcal/mol, respectively. Variation of substituents on the sulfur atoms is a convenient tool for fine tuning of the ligand properties and controlling the strength of the complex. The bite angle of the ligands does not depend on the substituent nature and is 88–89°, which is typical of square-planar complexes. According to the bite angle, the examined ligands are analogs of well known bidentate phosphine ligands, but the former are more labile since the corresponding binding energy is lower by 36 kcal/mol.

General Procedure of Pd-Catalyzed Selective Hydrophosphorylation of Alkynes

A novel catalytic system has been developed to accomplish the hydrophosphorylation of terminal and internal alkynes with high isolated yields (up to 96%) and excellent regio- and stereo­selectivity (>99:1). The key factor was to apply a low-ligated palladium/triphenylphosphane (1:2) catalytic system in the presence of a catalytic amount of trifluoroacetic acid. The catalytic system so developed has been applied successfully to permit the formation of diverse alkenylphosphonates utilizing a variety of available H-phos­phonates and alkynes.

Catalyst Leaching - an Efficient Tool for Constructing New Catalytic Reactions. Application to the Synthesis of Cyclic Vinylsulfides and Vinylselenides

Catalyst leaching from Pd and Ni particles stabilized by organic sulfur and selenium ligands occurs in solution in the presence of phosphanes. This process has been monitored in real time by 1D and 2D NMR spectroscopy and the nature of the metal species established. This catalyst leaching is shown to be a powerful tool for generating new catalytic activity from species formed in situ where the parent bulk particles are inactive. The catalytic system developed has been successfully implemented in a novel synthetic procedure that provides new types of cyclic sulfur and selenium compounds in high yields through the reaction between alkynes and dichalcogenides.

In the present review we address scarcely studied application area of NMR spectroscopy — investigation of molten state and solvent-free systems. In such a case NMR spectra are recorded without a solvent and without magnetic field stabilization on any nucleus. Taking our recent studies of catalytic addition of sulfur- and selenium-containing compounds to alkynes as examples, we describe most important practical aspects of NMR studies and their application for solving important chemical problems.

Stereodefined Synthesis of a New Type of 1,3-Dienes by Ligand-Controlled Carbon-Carbon and Carbon-Heteroatom Bond Formation in Nickel-Catalyzed Reaction of Diaryldichalcogenides with Alkynes

We have found that ligand control over the carbon−carbon and carbon−heteroatom bond formation on the nickel center provides an easy and convenient route to symmetrical (minor) and unsymmetrical (major) isomers of sulfur- and selenium-substituted 1,3-dienes. The unsymmetrical product is a new type of 1,4-substituted conjugated diene, which was readily synthesized from alkynes and diaryldichalcogenides. The unique feature of this developed one-pot transformation is total stereodefined synthesis of the diene skeleton, controlling not only the configuration of the double bond but also the
s-gauche conformation of the central C−C bond. The mechanistic study revealed the key feature of alkyne insertion into the Ni−E and Ni−C bonds (E = S, Se), which governs the direction of the chemical transformation.

We have developed two new catalytic systems based on Ni and Pd complexes to solve the challenging problem of dialkyldichalcogenide (Alk
2E2; E=S, Se) addition to alkynes. A comparative study of two catalytic systems — Ni/PMe2Ph and Pd/PCy2Ph — has revealed that the Ni catalyst is superior with respect to high catalytic activity and more general scope relative to the Pd system. A novel synthetic methodology was developed for the preparation of (Z)-bis(alkylthio)alkenes and (Z)-bis(alkylseleno)alkenes from terminal alkynes with excellent stereoselectivity and high yields.

New Approach for Size- and Shape-Controlled Preparation of Pd Nanoparticles with Organic Ligands. Synthesis and Application in Catalysis

A novel approach was developed to prepare Pd nanoparticles with organic ligands in high yields. The structural unit of the Pd species was constructed involving Pd−S bonds. The synthesized Pd particles were highly selective catalysts of S−H bond addition to alkynes under microwave heating. An X-ray diffraction study of one of the products of the addition reaction revealed unusual supramolecular organization of cation/anion layers.

Critical Effect of Phosphane Ligands on the Mechanism of Carbon-Carbon Bond Formation Involving Palladium(II) Complexes: A Theoretical Investigation of Reductive Elimination from Square-Planar and T-Shaped Species

A theoretical ONIOM study has been carried out to understand the influence of phosphane ligands on the structure of Pd complexes and their reactivity in C–C bond formation. The calculations were performed for Me–Me reductive elimination with the ligands L = PPh3, PCy3, PMe3, PH3, and vinyl–vinyl, Ph–Ph, ethynyl–ethynyl, vinyl–Me, vinyl–Ph and vinyl–ethynyl couplings with L = PPh3 for [PdR2Ln] complexes (n = 1, 2). The calculations revealed critical changes in the reactivity of palladium complexes depending on the mechanism and ligand type. In the case of the standard four-coordinate pathway (n = 2) the relative reactivity in carbon–carbon bond formation follows the order: L = PPh3 > PH3 > PCy3 > PMe3. However, for reductive elimination involving T-shaped complexes by the ligand predissociation pathway (n = 1), the relative reactivity changes in the order: L = PCy3 > PPh3 > PH3 > PMe3. The theoretical study suggested that the steric effect of phosphane ligands has the largest impact on the structure of the initial palladium complexes, while the electronic effect is most influential on the transition states of C–C coupling in these complexes.

Unusual Influence of the Structures of Transition Metal Complexes on Catalytic C-S and C-Se Bond Formation Under Homogeneous and Heterogeneous Conditions

In the presence of transition metal catalysts, hydrothiolation and hydroselenation reactions, as well as bisthiolation and bisselenation reactions, have been successfully carried out with high selectivities and yields. New transition metal-catalyzed synthetic methods have been developed for the preparation of vinyl sulfides and vinyl selenides of various types. Mechanistic study has revealed that a homogeneous catalytic system based on phosphine complexes of palladium is the best choice for carrying out stereoselective additions of disulfides and diselenides to alkynes. A heterogeneous Ni-catalyzed reaction with a unique self-organized nanostructured catalyst was superior for carrying out regioselective additions of thiols and selenols to alkynes

The synthetic application and mechanistic aspects of transition-metal (Ni, Pd, Pt) catalyzed addition of E-E and E-H (E=S, Se) bonds to alkynes were investigated in detail. This study revealed major factors controlling the selectivity of such addition reactions. A new Ni-based catalytic system with a self-organized nanostructured catalyst has been designed to perform chemical transformations in high yield, under mild conditions.

A simple heterogeneous Ni-based catalytic methodology was developed for regioselective hydroselenation of terminal alkynes and stereoselective hydroselenation of internal alkynes. The developed heterogeneous catalytic system is superior to the known homogeneous and heterogeneous catalysts for the Se−H bond addition to the triple bond of alkynes. The catalytic transformation was performed under mild conditions, thus avoiding byproducts formation. The mechanistic study revealed that the yield of the addition products depends on the catalyst particle size and rapidly increases upon decreasing particle size into the nanosized region. The present study describes a simple and efficient procedure for the formation of a self-organized nanosized catalytic system starting from an easily available precursor, Ni(acac)2, without any special treatment.

Nickel-Catalyzed Addition of Benzenethiol to Alkynes: Formation of Carbon-Sulfur and Carbon-Carbon Bonds

Nickel-catalyzed addition of benzenethiol to alkynes leads to alkenyl and dienyl sulfides; the direction of the process can be controlled by varying the PhSH/alkyne ratio. An advanced procedure, which ensures higher yields of 2-phenylsulfanylalkenes, includes gradual addition of alkyne to the other reactants. The structures of conjugated dienyl sulfides formed in the reaction were determined by 2D NMR spectroscopy.

Homogeneous Nickel Catalysts for the Selective Transfer of a Single Arylthio Group in the Catalytic Hydrothiolation of Alkynes

A novel homogeneous catalytic system has been developed for the regioselective hydrothiolation of alkynes based on CpNi(NHC)Cl complexes (NHC = N-heterocyclic carbene). The designed catalyst was efficient for the selective addition of a single ArS group to an alkyne and was suitable for the synthesis of vinylsulfides, without side reactions leading to bis(arylthio)alkenes. Furthermore, this catalytic system allowed for the S−H bond addition to alkynes to be performed with high regioselectivity (up to 31:1) and in good yields (61−87%). A mechanistic study showed that this reaction involved three steps: (1) a nickel-based substitution of chloride for the ArS group, (2) alkyne insertion into the Ni−S bond, and (3) protonolysis of the Ni−C bond. The intermediate CpNi(NHC)(SAr) complexes were unambiguously characterized by X-ray analysis.

An Efficient and Convenient Synthesis of beta-Vinyl Sulfides in Nickel Catalyzed Regioselective Addition of Thiols to Terminal Alkynes Under Solvent Free Conditions

A new nanosized catalytic system has been developed for convenient preparation of β-vinyl sulfides H2CC(SAr)R with high yields (79−98%) and excellent selectivity (>98:2). Inexpensive and easily available Ni(acac)2 was used as catalyst precursor. Solvent-free conditions were combined with high atom efficiency of the ArSH addition reaction to terminal alkynes (HC⋮C−R) in order to create an environmentally friendly synthetic procedure. The mechanistic study has indicated that catalytic reaction takes place under heterogeneous conditions with alkyne insertion into the Ni−S bond as a key step.

The first example of palladium-catalyzed stereoselective addition of diphenyl disulfide and diphenyl diselenide to the triple bond of terminal alkynes under microwave irradiation conditions is described. It was found that both the element—element (E-E) and carbon—element bonds can be activated in the catalytic system studied. The products of both reactions were isolated in quantitative yields. According to quantum-chemical calculations, the reaction mechanism involves the oxidative addition of the E-E bond to Pd0. Depending on the microwave power and reaction conditions, the next stage is either the reaction with alkyne or the carbon—element bond activation. The product of the oxidative addition of Ph2Se2 to Pd0, namely, dinuclear complex [Pd2(SePh)4(PPh3)2], was detected by 31P{1H}NMR spectroscopy directly in the Ph2Se2/PPh3 melt formed under microwave irradiation conditions.

Theoretical Insight into the C-C Coupling Reactions of the Vinyl, Phenyl, Ethynyl, and Methyl Complexes of Palladium and Platinum

The mechanism and controlling factors of the C−C reductive elimination reactions of vinyl, phenyl, ethynyl, and methyl ligands from the Pd and Pt complexes RR'M(PH3)2 were studied with a density functional method. The barrier of C−C coupling from the symmetrical R2M(PH3)2 (where M = Pd, Pt) complex decreases in the order R = methyl > ethynyl > phenyl > vinyl, and the exothermicity of the reaction increases in the same order. That is, the methyl−methyl coupling has the highest barrier and smallest exothermicity, while the vinyl−vinyl coupling has the smallest barrier and largest exothermicity. For the asymmetrical RR'M(PH3)2 complexes, the activation and reaction energies are found to be approximately the average of the corresponding parameters of symmetrical coupling reactions, and this simple rule is expected to be valid for other asymmetrical coupling reactions involving different substituted alkyl, vinyl, phenyl, and ethynyl groups as well as different transition-metal complexes. These C−C coupling reactions occur much more easily in Pd than in Pt complexes, because the Pd−R bonds are weaker than the Pt−R bonds. The major thermodynamic and kinetic factors determining the C−C coupling in these complexes have been discussed. For reactions with similar exothermicities, the kinetics of C−C bond formation is mainly determined by the orientation effect that includes the directionality of the M−C bond and the steric interaction between R and the other ligand (phosphine in the present case), which favors vinyl over phenyl over methyl. However the activation barrier is strongly dominated by exothermicity when it is very different between reactions.

New Catalytic System for S-S and Se-Se Bond Addition to Alkynes Based on Phosphite Ligands

A new catalytic system for the Ar2E2 (E = S, Se) addition to terminal alkynes (HC⋮C−R) has been developed to synthesize bis-element-substituted alkenes Z-H(ArE)CC(EAr)R with high stereoselectivity and yields. Utilizing phosphite ligand P(OiPr)3 allowed solving two major problems of this catalytic reaction: (1) prevent catalyst polymerization and (2) simplify product purification procedures. Key intermediatestrans-[Pd(SPh)2(P(OiPr)3)2] and trans-[Pd2(SPh)4(P(OiPr)3)2]were synthesized by S−S oxidative addition reaction to Pd(0) and studied by X-ray analysis. The equilibrium between the mononuclear and dinuclear complexes in solution was established by 31P NMR spectroscopy. In addition to the advantages in the synthetic procedure, the isolation of the stable palladium complexes with phosphite ligand made possible a detailed mechanistic study of the catalytic reaction.

The First Example of Polymer-Supported Palladium Catalyst for Stereoselective S-S Bond Addition to Terminal Alkynes

The polymer-supported recyclable palladium catalyst was prepared for stereoselective diaryl disulfides addition to ­terminal alkynes with high yields. The 96-98% product purity was achieved after filtering the polymer-supported catalyst without ­special purification procedure.

The main concept behind the new procedure involves joint analysis of HMQC spectral data and theoretically calculated NMR chemical shifts. Using the combined experimental/ab-initio methodology, complete signal and stereochemical assignments were made for the isomers in HMQC spectrum. Chemical shifts of 77Se were calculated with GIAO method at B3LYP/6-311G(d) level with good accuracy.

NiCl2 Catalyzed Regioselective Hydrothiolation of Alkynes

Regioselective Markovnikov-type addition of PhSH to alkynes (HC≡C-R) has been performed using easily available nickel complexes. The non-catalytic side reaction leading to anti-Markovnikov products was suppressed by addition of γ-terpinene to the catalytic system. The other side reaction leading to the bis(phenylthio)alkene was avoided by excluding phosphine and phosphite ligands from the catalytic system. It was found that catalytic amounts of Et3N significantly increased the yield and selectivity of the catalytic reaction. Under optimized conditions high product yields of 60–85% were obtained for various alkynes [R=n-C5H11, CH2NMe2, CH2OMe, CH2SPh, C6H11(OH), (CH2)3CN]. The X-ray structure of one of the synthesized products is reported.

Can Steric Effect Induce the Mechanism Switch in the Rhodium Catalyzed Imines Boration Reaction? A Density Functional and ONIOM Study

Combined density functional and ONIOM studies have been performed to investigate the mechanism of rhodium-catalyzed boration of imines. Catalytic imine boration has been found to proceed via the following stages: (1) oxidative addition of B−B to the Rh complex, (2) imine coordination, (3) migratory insertion of the imine into the rhodium−boron (Rh−B) bond, and (4) β-hydrogen elimination to give a monoboration product or carbon−boron (C−B) bond formation to yield a diboration product. The choice of the final stage depends on the structure of the imine and boration reagent. Bulky substrate molecules facilitate C−H bond activation and retard C−B bond formation, while in the absence of sterical hindrance C−B bond formation is preferred over C−H bond activation. The present study is the first that outlines the mechanistic differences in C
C and CN bond boration and rationalizes the effect of bulky substituents on the mechanism of imine boration reaction. The expected difference in regioselectivity between imine and alkene boration is also discussed.

Evaluation of 13C NMR Spectra of Cyclopropenyl and Cyclopropyl Acetylenes by Theoretical Calculations

A convenient methodology was developed for a very accurate calculation of 13C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of 13C NMR chemical shifts. In addition, the particular dependencies of 13C chemical shifts on the geometry of cyclopropane ring were investigated.

An efficient methodology was developed for performing palladium-catalyzed E–E (E = S, Se) bond addition to alkynes under solvent free conditions. Compared to reaction in solvent significant enhancement of reaction rate, improved efficiency and remarkable catalyst stability were observed under solvent free conditions. The addition reactions were carried out with high stereoselectivity and yields in a short reaction time.

Solvent-free palladium-catalyzed addition of diaryl disulfides and diselenides to terminal alkynes makes it possible to achieve high stereoselectivity and almost 100% yields in ≈10 min using only 0.1 mol.% catalyst. Both Pd(PPh
3)4 and easily available Pd(OAc)2 and PdCl2 can be used in the reaction with an excess of triphenylphosphine. The catalyst and triphenylphosphine are readily recycled for repeated use. The study of the mechanism of the solvent-free catalytic reaction indicates that the process involves binuclear palladium complexes.

New Approach to Stereochemical Structure Determination of bis-Selenium-Subsituted Alkenes

A new approach to determination of the stereochemical structure of bis-selenium-substituted alkenes using experimental
77Se NMR studies and B3LYP/6-311G(d) quantum-chemical calculations is developed. Joint analysis of experimental and calculated data allows assignment of signals in the 77Se NMR spectrum. The method was evaluated taking the model compounds (PhSe)HC=C(SePh)R (R = COOMe, CH2NMe2, CH2OH, Ph) as examples.

A mechanistic study of the hydroselenation of alkynes catalyzed by Pd(PPh
3)4 and Pt(PPh3)4 has shown that the palladium complex gives products of both Se-H and Se-Se bond addition to the triple bond of alkynes, while the platinum complex selectively catalyzes Se-H bond addition. The key intermediate of PhSeH addition to the metal center, namely Pt(H)(SePh)(PPh3)2, was detected by 1H-NMR spectroscopy. The analogous palladium complex rapidly decomposes with evolution of molecular hydrogen. A convenient method was developed for the preparation of Markovnikov hydroselenation products H2C-C(SePh)R, and the scope of this reaction was investigated. The first X-ray structure of the Markovnikov product H2C-C(SePh)CH2N+HMe2HOOC-COO− is reported.

Mechanistic Investigation and New Catalyst Design in Palladium and Platinum Catalyzed Se-Se Bond Addition to Alkynes

The present study explains the different catalytic activities of platinum and palladium in Se−Se addition reactions with alkynes. Under the catalytic conditions
cis-[Pt(SePh)2(PPh3)2] undergoes fast isomerization to the trans isomer, which does not react with alkynes. Palladium complexes maintain their catalytic activity, due to the formation of the dinuclear structure [Pd2(SePh)4(PPh3)2]. It was shown that the palladium intermediate involved in the catalytic cycle can be prepared directly in the reaction mixture starting from the simple [PdCl2(PPh3)2] precursor, thus allowing replacement for the traditional Pd(PPh3)4 catalyst. X-ray analysis shows that the products of Se−Se addition reactions with alkynes possess the necessary geometry parameters for coordination as bidentate ligands.

The mechanistic study of palladium catalyzed S–S and Se–Se bonds addition to alkynes revealed the involvement of dinuclear transition metal complexes in the catalytic cycle. Coordination of alkyne to dinuclear transition metal complex was found to be the rate determining step of the reaction. An unusual phosphine ligand effect increasing the yield of addition reaction was found in the studied system. A new synthetic procedure was developed to perform the catalytic reaction using easily available Pd(II) complex. The scope of the reaction and the reactivity of S–S and Se–Se bonds toward alkynes were investigated. The X-ray structure of the product of S–S bond addition reaction showed favorable geometry for the possible application as a chelate ligand.

An unusual phosphine ligand effect increasing the yield of the Ar
2E2 addition reaction to alkynes was found. The catalytic reaction involves intermediate formation of dinuclear palladium complexes, which may be a subject of further polymerization.

Stereo- and Regioselective Functionalization of Alkynes Catalyzed by Platinum(IV) and Palladium(II) Complexes in the System I--I3--H2O/MeOH

Activation of the CÍÄC bond in acetylenic hydrocarbons, catalyzed by iodide complexes of platinum(IV), and the subsequent CÄC coupling reaction make it possible to synthesize 1,4-diiodo-substituted dienes with high stereo- and regioselectivity. The reaction involves intermediate formation of bis-σ-vinyl platinum(IV) complexes which can be isolated in the pure state. Under similar conditions palladium(II) complexes catalyze iodine addition to acetylene.

Mechanistic Study of Catalytic Phenylselenol Addition to Alkynes

Addition of benzeneselenol to terminal alkynes HC:CR, catalyzed by Pd(0) complexes, leads to formation of mixtures of mono- and bis(phenylseleno)alkenes, depending on the nature of the R substituent. Electron-donor groups (R = Bu, CH2OH, CH2NMe2) give rise to addition according to the Markovnikov rule, whereas from alkynes with electron-acceptor groups (R = Ph, COOMe) mixtures of products are formed as a result of side reactions. A probable reaction mechanism includes oxidative addition of benzeneselenol to the metal, alkyne insertion into the Pd-Se bond, and reductive elimination.

A detailed density functional study was performed for the vinyl−vinyl reductive elimination reaction from bis-σ-vinyl complexes [M(CH
CH2)2Xn]. It was shown that the activity of these complexes decreases in the following order: PdIV, PdII > PtIV, PtII, RhIII > IrIII, RuII, OsII. The effects of different ligands X were studied for both platinum and palladium complexes, which showed that activation barriers for C−C bond formation reaction decrease in the following order: X = Cl > Br, NH3 > I > PH3. Steric effects induced either by the ligands X or by substituents on the vinyl group were also examined. In addition, the major factors responsible for stereoselectivity control on the final product formation stage and possible involvement of asymmetric coupling pathways are reported. In all cases ΔE, ΔH, ΔG, and ΔGaq energy surfaces were calculated and analyzed. The solvent effect calculation shows that in a polar medium halogen complexes may undergo a reductive elimination reaction almost as easily as compounds with phosphine ligands.

The mechanisms of intermolecular and intramolecular enyne [4 + 2] cycloaddition reactions were investigated in detail using high-level
ab initio methods. The structures of all transition states and intermediates were located using the MP2 method, potential energy surfaces were calculated at the MP2, MP3, MP4(SDQ), MP4(SDTQ), CCSD and CCSD(T) theory levels and the solvent effect was studied within PCM model.

Stable Pt(IV) Vinylic Complexes with Unusual Regioselectivity Formed in the Reaction of Methylpropiolate Triple Bond Activation

An unusual fact of HC-C-COOMe triple bond activation by Pt(IV) iodide leading to the formation of new bis-σ-vinyl complexes [Pt(CH-CI-COOMe)(CIH-C-COOMe)(Sol)
3−nIn]2−n (where n=2, 3) with different regioselectivity in vinyl ligands is reported. The isolated complex can be involved in C–C coupling reaction resulting in a head-to-tail connection of vinyl groups in a substituted diene unit.

A density functional theoretical study has been performed for the mechanisms of platinum(IV)-catalyzed alkyne-to-conjugated diene conversion reaction, which involves two subsequent triple bond activation steps followed by vinyl−vinyl coupling. Calculations have shown that acetylene triple bond activation by PtI
62- in water or methanol solution may proceed through either external nucleophile addition or intramolecular insertion, with the former mechanism occurring with a lower barrier and leading to thermodynamically favored product. The rate-determining step of the entire catalytic cycle is found to be the formation of a platinum(IV) cis-divinyl derivative. Although vinyl−vinyl coupling reaction may take place from both six-coordinated octahedral and five-coordinated square-pyramidal platinum(IV) divinyl complexes, the five-coordinated derivative was found to react with a significantly lower barrier. The results obtained here are in good agreement with available experimental data and reveal important details of the catalytic reaction mechanism. The present investigation also has shown that no reliable conclusions may be drawn for the system studied without taking solvent effects into account.

An unusual fact of C-C reductive elimination reaction in bis-chelated Pt(IV) complexes under mild conditions was studied. It has been shown that breaking at least one of the chelate rings is required to promote a carbon-carbon bond formation reaction. An intermediate complex, which resulted from a chelate ligand breaking process, was detected directly in the reaction mixture using 2D
1H–195Pt heteronuclear NMR spectroscopy.

Synthesis and Structure of [Pt(CH=CI-CH2OCH3)2(I)2] as Possible Intermediate of Catalytic Alkynes Conversion Reaction into Diiodosubstituted Dienes

Direct evidence was found that catalytic alkynes conversion reaction in the system Pt(IV)-I
−-I2 proceeds through a platinum(IV) σ-vinyl complex. A synthesis, X-ray structure determination, and a multinuclear NMR study of the key-intermediate complex [Pt(CH-CI- CH2OCH3)2(I)2] as well as an expansion of the catalytic reaction are shown.

A Novel Stereoselective and Catalytic C-C coupling Reaction: Acetylene Dimerization Accompanied by Addition of Iodine to Yield (E,E)-1,4-Diiodobutadiene-1,3 in the PtIV-I--I2-MeOH System

A new catalytic reaction – dimerization of acetylene accompanied by addition of iodine to yield (E,E)-1,4-diiodobuta-1,3-diene at 30°C in a methanolic solution of NaI, PtIV and I2 – has been found; a plausible reaction mechanism involves intermediate formation of a cis-divinyl derivative of platinum(IV) through two subsequent triple bond iodoplatination steps followed by reductive elimination of the final product.